Generic revision and species classification of the Microdontinae (Diptera, Syrphidae)

Abstract With 552 species group names available (excluding misspellings), the Microdontinae constitute the smallest of the three subfamilies of Syrphidae. Paradoxically, this subfamily is taxonomically the least organized of the three: 388 species names were previously classified in a single genus, Microdon Meigen, 1803. The present paper introduces a new generic classification of the Microdontinae, relying partly on the results of phylogenetic analyses of morphological and molecular data as published in other papers, and partly on examination of primary type specimens of 347 taxa, plus additional material, and original descriptions. A total number of 67 genus group names (excluding misspellings) are evaluated, redescribed, diagnosed and discussed, with several implications for their taxonomic status. Of these, 43 names are considered as valid genera, 7 as subgenera, 17 as synonyms. Two generic names (Ceratoconcha Simroth, 1907, Nothomicrodon Wheeler, 1924) are left unplaced, because they are known from immature stages only and cannot be reliably associated with taxa known from adults. The following 10 new genera are described by Reemer: Domodon, Heliodon, Laetodon, Menidon, Mermerizon, Metadon, Peradon, Piruwa, Sulcodon and Thompsodon. A key to all genera, subgenera and species groups is given. A total number of 26 new species are described in the following genera: Archimicrodon Hull, 1945, Ceratrichomyia Séguy, 1951, Domodon, Furcantenna Cheng, 2008, Heliodon, Indascia Keiser, 1958, Kryptopyga Hull, 1944, Masarygus Brèthes. 1908, Mermerizon, Metadon, Microdon, Paramixogaster Brunetti, 1923, Piruwa, Pseudomicrodon Hull, 1937, Rhopalosyrphus Giglio-Tos, 1891, and Thompsodon. New lectotypes are designated for Ceratrichomyia behara Séguy, 1951 and Microdon iheringi Bezzi, 1910. A total number of 267 new combinations of species and genera are proposed. New synonyms are proposed for 19 species group names. Three replacement names are introduced for primary and secondary junior homonyms: Microdon shirakii nom. n. (= Microdon tuberculatus Shiraki, 1968, primary homonym of Microdon tuberculatus de Meijere, 1913), Paramixogaster brunettii nom. n. (= Mixogaster vespiformis Brunetti, 1913, secondary homonym of Microdon vespiformis de Meijere, 1908), Paramixogaster sacki nom. n. (= Myxogaster variegata Sack, 1922, secondary homonym of Ceratophya variegata Walker, 1852). An attempt is made to classify all available species names into (sub)genera and species groups. The resulting classification comprises 454 valid species and 98 synonyms (excluding misspellings), of which 17 valid names and three synonyms are left unplaced. The paper concludes with a discussion on diagnostic characters of Microdontinae.


Introduction
The Microdontinae (Diptera: Syrphidae) are found on all continents except Antarctica. The vast majority of more than 400 described species occurs in the tropics, of which almost half in the Neotropics. With little more than 50 species known from the Holarctic region, the group is relatively poorly represented in temperate regions. This partly explains why the taxonomy of the group has so far received little attention compared to other Syrphidae. This can also be explained by the morphological variation within the Microdontinae, which is arguably larger than in many families of Diptera Cyclorrhapha. Several authors have commented on the group's paradoxical combination of a wealth of morphological diversity at the species level and a scarceness of groupdefining characters (Bezzi 1915, Curran 1941, Shannon 1927. As a result, more than 300 out of approximately 400 valid species names are classified currently in the single genus Microdon . This apparent taxonomic indecisiveness seems to result not so much from a lack of morphological variation, but rather from an excess of it. The classification of taxa, generic as well as specific, within the Microdontinae is the subject of the present paper. All available generic taxa of Microdontinae, as well as many species, are studied and compared in detail. Although phylogenetic relationships are still unclear for many taxa, we prefer to employ an 'old-fashioned' method of classification based on detailed comparative morphology over a 'waste basket' approach, despite their morphological differences (for more on this see Procedure under Material and Methods). A first phylogenetic analysis of the group is in press (Reemer and Ståhls in press), and in a number of instances the results of that study will be referred to.

Classification of Microdontinae within Syrphidae
When  introduced the generic name Microdon, there was no intrafamilial classification of the family Syrphidae. The first family group name proposed for Microdon and its allies was Aphritadae Fleming, 1821(spelled Aphritidae by Fleming 1822, separated from the 'Syrphadae' based on the absence of a facial tubercle. The Aphritidae also included Milesia Latreille, 1804 and related genera, which are nowadays included in the Eristalinae. Although the family group name Aphritidae has priority over Microdontinae, the latter name is maintained because Aphritidae has not been used after 1899, whereas Microdontinae has been used by many authors since (ICZN 1999: article 23.9, Sabrosky 1999. Rondani (1845) first introduced the family group name Microdontinae (spelled as 'Microdonellae'), based on the dentate scutellum of the type species Microdon mutabilis Linnaeus, 1758. Ever since, this group has been recognized as distinct from other Syrphidae, albeit under different spellings and taxonomic rankings. In early days (Lioy 1864, Brauer 1883, Williston 1886) and the single more recent case of Shatalkin (1975a, b), authors included genera which are nowadays considered to belong to other subfamilies. The placement of the group relative to other Syrphidae, however, has been far from stable. It would exceed the aim of the present paper to repeat here every author's argumentations for their subsequent classifications over more than one and a half century. Table 1 lists the many different historical taxonomic treatments (spellings and classifications) the group has received.
The first to regard the Microdontinae as "presumably an old group early differentiated from the family" was Hull (1949). Goffe (1952) extensively reviewed the prior classifications of Syrphidae, including Microdontinae.
He placed the Microdontinae as a subtribe ('Microdontina') in the tribe Volucellini, together with the subtribe Volucellina, as part of the subfamily Sphixinae (more or less equivalent to the current Eristalinae). Thompson (1969) did not agree and treated the group again as basal within the Syrphidae. Then Thompson (1972) proposed to raise the group to family level. Shatalkin (1975a, b) did not follow this proposal, basing his argumentation only on the number of male pre-abdominal segments, but he agreed on the basal position of the group as a subfamily within the Syrphidae.
The proposal of Thompson (1972) to treat the Microdontinae as a separate family has not generally been followed. Speight (1987), however, based on his considerations of syrphid morphology, found Microdon to be aberrant from other Syrphidae to such an extent that he chose to follow Thompson's proposal. In the study of Rotheray and Gilbert Table 1. Chronological overview of spellings, classifications and rankings of the family group names Aphritadae Fleming, 1821 andMicrodonellae Rondani, 1845. All known references introducing a novel spelling or classification are included, as well as all known works that explicitly deal with the classification of the group. Works merely using previously suggested classifications are omitted. (1999), based on characters of immature stages, Microdontinae were placed as follows: (Eristalinae + (Microdontinae + (Syrphinae + Pipizini)). Subsequently, a number of studies recovered the Microdontinae as the sister-group of all other Syrphidae: Skevington and Yeates (2000) (based on molecular data), Ståhls et al. (2003) (based on molecular data combined with larval and adult morphology), and Rotheray and Gilbert (2008) (based on characters of the larval head). The results of Hippa and Ståhls (2005) (based on an extended set of adult morphological characters) differed from those previously mentioned by the placement of (Neoascia Williston, 1886+ Sphegina Meigen, 1822 as sister-group to all other Syrphidae. However, all of these authors treated the Microdontinae as a subfamily, as did Cheng and Thompson (2008). Speight (2010) has, however, continued to use familial rank. Reemer and Ståhls (in press), evaluating previous phylogenetic results as well as their newly generated evidence, see no scientific reason for changing the prevailing ranking of the Microdontinae and for that reason prefer nomenclatural stability.

Classifications and phylogenetic relationships within Microdontinae
There have been few previous attempts to generate a tribal classification of Microdontinae. Apart from the names Aphritidae Fleming and Microdontinae Rondani (see previous paragraph), only three family-group names have been proposed: Masarygidae Brèthes, 1908, Ceratophyini Hull, 1949 and Spheginobacchini Thompson, 1972. See Reemer and Ståhls (in press) for discussion on availability of these names. Application of the first two names is at present considered undesirable, as most phylogenetic relationships at suprageneric level are still too uncertain to recognize tribes, due to limited availability of taxa for molecular phylogenetic analysis and the obtained low support values for most of the resolved larger clades (Reemer and Ståhls in press). The tribe Spheginobacchini is the only of these names that continues to be recognized here, as we consider the sister group relationship of this taxon to the remaining Microdontinae well enough established (Ståhls et al. 2003, Reemer and Ståhls in press). Cheng and Thompson (2008) gave an extensive overview of generic names of Microdontinae, which formed the starting point for the present paper. Since  introduced the name Microdon, 59 genus-group names applicable to Microdontinae have been introduced (misspellings excluded) (Fig. 1). This number increased most rapidly during the first half of the 20th century. Since then, only nine new genusgroup names have been proposed. The number of previously introduced species-group names in Microdontinae is 514 (including synonyms and unvalid names). The cumulative graph of the number of species names per decade is similar to the one for genus-group names (Fig. 2). A majority of these species names (388) are currently classified into the genus Microdon. Most of the other (sub)genera contain only a few species. The very large genus Microdon thus constitutes one of the greatest taxonomic challenges of Syrphidae. The classification of so many species into one genus was a consequence of pragmaticism, as no comprehensive revisions were available.

Procedure
The phylogenetic results of Reemer and Ståhls (in press) are used as a first cue for the generic classification. When the evidence provided by these analyses is not conclusive or considered unconvincing (e.g. because of low support values), morphological characters are evaluated subjectively. Considerable weight is given to the structure of the male genitalia, but in all cases there are also external characters to support the groups. The species classification relies largely on this morphological evaluation.
Generally, a conservative approach is adopted towards changing the rank of taxa. Generic or subgeneric ranks as indicated by Cheng and Thompson (2008) are mostly maintained, unless these are contradicted by the results of the phylogenetic analyses of Reemer and Ståhls (in press). This is mainly relevant in the case of the genus Microdon. The species previously assigned to this genus were resolved as scattered over the phylogenetic trees of Reemer and Ståhls (in press). For some of these groups, genus group names are available, for some there are none. In several cases, genus group names that were previously treated as subgenera are now raised to generic level. In addition, new genus group names needed to be erected for several taxa that were previously included in Microdon. Given the uncertainties in the deeper branches of Microdontinae-phylogeny, these new group names could also have been given subgeneric rank within Microdon. However, this would suggest a close affinity with that genus, despite the fact that this is not indicated by the phylogenetic results. Moreover, we found it useful to split the genus Microdon into smaller natural groups which are more manageable than a genus containing more than 300 species. As this is only done for groups which have a high probability of being monophyletic (as indicated by phylogenetic results of Reemer and Ståhls (in press) or by subjective judgement of supposed synapomorphies), this procedure will facilitate further research on intergeneric phylogenetic relationships. Wing with conspicuous black markings in apical half (Fig. 230)  Metallic green species, mimics of chrysidid wasps (Fig. 63, 64 Basoflagellomere more than three times as long as scape; with long pilosity in male (Fig. 325)  Abdomen narrow: more than 1.5 times as long as wide (Figs 163, 167) ....Metadon -Abdomen wide: less than 1.5 times as long as wide (Fig. 181)  Tergites 3 and 4 not fused, able to articulate independently (Fig. 120). Male: sternite 4 not visible in ventral view: completely covered by sternite 3 and lateral margins of tergites (Fig. 123). Male basoflagellomere with long pile (Fig. 122)  Tergite 2 at most as long as anterior width (Fig. 81)  Vertex convex, shining, sparsely pilose to bare (Fig. 310, 315) ...Pseudomicrodon -Vertex more or less flat, dull and entirely pilose (Fig. 339, 344 Face with median tubercle on dorsal half (Fig. 31)  Vein M1 more or less straight, not parallel to wing margin, making straight angle with vein R4+5 (Fig. 14, 166, 219 Antenna at least as long as distance between antennal fossa and anterior oral margin, furcate in male (Figs 39,77,138,144,(356)(357)(358)(359)(360)(361)  Position of crossvein r-m at same level as bm-cu (Fig. 258)  Antenna longer than distance between antennal fossa and anterior oral margin. Basoflagellomere more than 3 times as long as wide (Figs 269-277) ......... Paramixogaster (in part: P. decipiens (de Meijere) and undescribed Australian sp.) -Antenna shorter than distance between antennal fossa and anterior oral margin. Basoflagellomere less than 2 times as long as wide (Figs 301,302,306) . Abdomen oval or more or less parallel-sided, not constricted (Fig. 330). Occiput without creases (Fig. 328)

Order and format
The genera accounts are presented in alphabetic order. Accounts are only given for taxa considered as valid genera or subgenera. Synonyms and misspelled names can be found under the valid genera to which they belong. Each group account starts with information on the original description and the type species. This is followed by the following components. Description. Body length (intended only as an approximation, as not all specimens have been measured). A short characterization of the habitus is given, followed by a general description, which is intended to give characters considered (potentially) useful for identification, and to indicate the variability of characters. Unless stated otherwise, all listed characters apply to both sexes. Illustrations are given to illustrate habitus, important external characters and male genitalia. Additional morphological characters can be found in the character matrix of Reemer and Ståhls (in press).
Diagnosis. The shortest possible enumeration of external characters considered sufficient to distinguish the genus from all other Microdontinae. Characters of the male genitalia are only given in a few cases. The combination of the given characters is necessary for the diagnosis; all characters not given are considered unnecessary for this purpose. In some cases this diagnosis will not add much to the characters given in the key, but in other cases it will provide a 'short-cut' to the recognition of the genus.
Discussion. Arguments are given for the proposed classification. Other comments are given when necessary, e.g. on type specimens, history of classification, and morphological characters.
Diversity and distribution. The number of described species is given, sometimes with a speculation on the possible number of undescribed species. When available, a reference to species keys is given. The known geographic range is indicated.
Etymology. Only given for newly described genera.

Afromicrodon
Thompson http://species-id.net/wiki/Afromicrodon Figs 3-6 Afromicrodon Thompson, 2008: 26 (in Cheng andThompson 2008 Diagnosis. Abdomen oval. Antenna shorter than distance between antennal fossa and anterior oral margin. Postpronotum pilose. Postero-apical corner of cell r4+5 rectangular. Proepimeron bare. Anepisternum widely bare medially, also on dorsal half. Anepimeron entirely pilose. Vein R4+5 usually with posterior appendix; if not: thorax and abdomen entirely black. Discussion. Archimicrodon was described as a subgenus of Microdon by , and considered as such by subsequent authors, including Cheng and Thompson (2005), who stated that three species are included. Most of the species assigned to Archimicrodon in the present paper were previously placed in Microdon. However, they do not agree with the more strict definition of Microdon used here. Its independent position from Microdon and its monophyly are supported by the phylogenetic results of Reemer and Ståhls (in press). These are reasons to raise Archimicrodon to generic status.
Three groups are recognized within this genus: Archimicrodon s.s., the subgenus Hovamicrodon, and a 'leftover' group, here called Archmicrodon s.l. Archmicrodon s.s. is based on A. simplicicornis (de Meijere, 1908), a subjective senior synonym of the type species of the genus, Microdon digitator Hull, 1937 syn. n. Archimicrodon s.s. is here defined by the shape of the surstylus: more or less oval, without a long posterior process ( Fig. 9, 15); scutellar calcars are either present or absent, but never spatulate. The subgenus Hovamicrodon is defined (following Keiser 1971) by the spatulate shape of the scutellar calcars (Fig. 18); the surstylus has a long posterior process (Fig. 19). Archimicrodon s.l. is here defined as containing all other species, in which the scutellar calcars are absent or -if present -not spatulate, and in which the surstylus has a long posterior process . As far as the African species are concerned, this group corresponds with the brevicornis-group of Bezzi (1915).
The three groups are very similar in their morphology, except for the small differences as noted above. It seems likely that the groups are closely related. The subgenus Hovamicrodon is probably monophyletic, considering the spatulate scutellar calcars in combination with its restricted distribution (Madagascar). However, as the phylogenetic analyses by Reemer and Ståhls (in press) indicate, it is so closely related to Archimicrodon s.l. (which is recovered as paraphyletic with respect to Hovamicrodon) that a separate generic status seems not warranted. Besides, a spatulate shape of the scutellar calcars can also be found in certain species of the New World genera Laetodon gen. n. and Serichlamys Curran, 1925. The latter genus is recovered as sister to Archimicrodon by Reemer and Ståhls (in press). As this character is not unique, it does not provide sufficient basis to base a genus on.
Sexual dimorphism can be pronounced, especially in the African species of this group (including Hovamicrodon). Females tend to be much larger than males, and are different in colouration (usually darker). As several species were described from one sex only (such as certain Madagascar species described by Keiser 1971), it is possible that some of these species are actually synonyms. However, as many taxa are represented by only one specimen, these matters cannot yet be resolved.
Hova is the name of one of the social castes of the Merina, an ethnic group indigenous to Madagascar. Keiser (1971) used this name for his genus Hovamicrodon. Surprisingly, he did not include the Madagascar species Microdon hova Hervé-Bazin, 1913 in this genus, although this species clearly belongs to this group (spatulate scutellar calcars). Keiser (1971) does mention a specimen which he believes to be M. hova, based on the description, but for some reason this species is not listed under Hovamicrodon. However, when Keiser died in 1969, his paper was not finished yet. It was published posthumously, after the manuscript was finished and submitted by E. Lindner. Therefore, it is seems possible that Keiser intended to include M. hova in Hovamicrodon.
Notes on species. In genitalia, Microdon browni Thompson, 1968 is similar to Archimicrodon s.l.: phallus short, apically furcate, with dorsobasal projection; hypandrium with bulb-like base; surstylus with two elongate lobes; epandrium without ventrolateral ridge. In external morphology, the only difference with Archimicrodon seems to be that the antennae are longer than the distance between the antennal fossa and the anterior oral margin. This character is considered not important enough for group definition, as antennal length is quite variable within many genera of Microdontinae. For these reasons, Microdon browni is here considered as a species of Archimicrodon s.l. The phylogenetic analysis of morphological characters by Reemer and Ståhls (in press) provides no further clue to the taxonomic affinities of this taxon.
Diversity and distribution. Described species: 45. Widely distributed in the Afrotropical, Oriental and Australasian regions, with one species known from the Eastern Palaearctic (A. simplex (Shiraki, 1930)). Archimicrodon s.s. is only known from the Oriental region. The number of species of Archimicrodon s.s. is not known, as the male genitalia of several species were not studied. The subgenus Hovamicrodon (six species) is restricted to Madagascar.  Curran, 1941: 252, by original designation. Protoceratophya Hull, 1949: 314. Type species: Ceratophya carpenteri Hull, 1945 by original designation. For synonymy see Cheng and Thompson (2008). Paraceratophya Fluke, 1957: 38 Cheng and Thompson (2008).

Aristosyrphus
Description. Aristosyrphus (Aristosyrphus). Body length: 6-18 mm. Slender flies, often with constricted abdomen. Head wider than thorax. Face convex or almost straight in profile; about as wide as an eye or narrower. Lateral oral margins not produced. Vertex flat. Occiput narrow over entire length. Eye bare. Eyes in male weakly converging at level of frons, with mutual distance 2 to 3 times the width of antennal fossa. Antennal fossa about as wide as high. Antenna longer or shorter than distance between antennal fossa and anterior oral margin; basoflagellomere longer than scape, oval; bare. Postpronotum pilose. Scutellum semicircular; without calcars. Anepisternum without or with weak sulcus; anteriorly pilose or bare, posteriorly pilose, with pile limited to dorsal half. Anepimeron entirely pilose. Katepimeron convex; bare. Wing: vein R4+5 without posterior appendix; vein M1 making acute angle with vein R4+5, anterior part or entire vein M1 parallel to wing margin; postero-apical corner of cell r4+5 angular, with small appendix; crossvein r-m located within basal 1/7 of cell dm, often very close to base. Abdomen elongate: slightly oval, parallel-sided or constricted at segment 2; more than twice as long as wide. Tergites 3 and 4 fused. Male genitalia: phallus unfurcate, straight or bent dorsad; ejaculatory hood apicodorsally separately developed from actual phallus into prong-like structure, which may be mistaken for dorsal aedeagal process, but does not contain a sperm-duct; apical part of hypandrium consists of two separate lobes (separated ventromedially); epandrium without ventrolateral ridge; surstylus furcate or unfurcate. Description. Aristosyrphus (Eurypterosyrphus) Body length: 8-14 mm. Slender flies with parallel-sided, constricted or kite-shaped abdomen. Head wider than thorax. Face more or less straight, with median tubercle on dorsal half; about as wide as an eye or narrower. Vertex flat. Occiput narrow over entire length. Eye bare. Eyes in male not or only slightly converging at level of frons, with mutual distance 4 to 5 times the width of antennal fossa. Antennal fossa about as wide as high. Antenna longer than distance between antennal fossa and anterior oral margin; basoflagellomere shorter or longer than scape, oval, sometimes appearing swollen: more than twice as wide as scape; bare. Postpronotum pilose. Scutellum semicircular; without calcars. Anepisternum without or with weak sulcus; pilose on dorsal half, bare ventrally. Anepimeron pilose on dorsal half, bare ventrally. Katepimeron convex; bare. Wing: vein R4+5 without posterior appendix; vein M1 making straight or acute angle with vein R4+5; postero-apical corner of cell r4+5 angular, with small appendix; crossvein r-m located around basal 1/3 of cell dm. Abdomen parallel-sided, constricted or kite-shaped; more than twice as long as wide. Tergites 3 and 4 fused. Male genitalia: phallus unfurcate, straight or bent dorsad; ejaculatory hood apicodorsally enveloping phallus; apical part of hypandrium consists of two separate lobes (separated ventromedially); hypandrium in some species with elongate ventromedian structure parallel to phallus Figs 32, 34), resembling the lingula of certain taxa of the subfamily Syrphinae; epandrium without ventrolateral ridge; surstylus furcate or unfurcate.
Diagnosis. Vein R4+5 without posterior appendix. Abdomen elongate and parallelsided or constricted. Postpronotum pilose. Mesoscutum with transverse suture incomplete. Antenna longer than distance between antennal fossa and anterior oral margin.
Aristosyrphus s.s. Vein M1 oblique, at least anterior half parallel to wing margin. Face evenly convex. Anepimeron entirely pilose. Crossvein r-m located around basal 1/3 of cell dm. Ejaculatory hood apicodorsally developed into prong-like structure, separate from actual phallus (phallus may seem furcate under casual observation, but ejaculatory hood does not contain sperm duct).
Eurypterosyrphus. Vein M1 oblique or straight. Face with median tubercle. Anepimeron bare on ventral half. Crossvein r-m located within basal 1/7 of cell dm. Ejaculatory hood apicodorsally enveloping phallus, not developed into separate, prong-like structure.
Discussion. Morphological variation within this group is large, especially in the male genitalia (Figs 29,(32)(33)(34). In some specimens of Aristosyrphus primus Curran, 1941 an anterior stump is present at vein M (Fig. 28). This character has always been used as diagnostic for Mixogaster (Hull 1954, Cheng andThompson 2008 Cheng and Thompson (2008) who wrote that the name was 'established for a Microdon species, which has a greatly elongate basoflagellomere'. Clearly the taxon does not belong to Microdon, because of the long basoflagellomere and the structure of the male genitalia (apically furcate phallus). These characters, combined with the bare postpronotum, suggest it might be related to Paramixogaster. However, the phylogenetic analysis of morphological characters by Reemer and Ståhls (in press) place it as a sister group of a clade containing taxa of which the male has a furcate basoflagellomere: Schizoceratomyia, Furcantenna and Carreramyia. Future studies employing molecular data could help elucidate the phylogenetic affinities of Bardistopus.
According to Mann (1920) the type specimens of the type species are females, but actually both are males (coll. USNM).
Diversity and distribution. Diagnosis. Hind tibia widened and with long, brush-like pilosity. Vein R4+5 without posterior appendix. Vertex strongly produced but not shining and convex. Basoflagellomere at least four times as long as scape, bifurcate in male.
Diversity and distribution. Described species: 2. Only the type species, Carreramyia megacephalus (Shannon, 1925), is known from more than one specimen (Panama and Costa Rica). The other species was found in Peru. Descriptions of two additional species from Peru and Surinam are in preparation by the first author. Apparently the genus is widespread in the Neotropical region. Discussion. Cheng and Thompson (2008) point out the confused taxonomic history of Ceratophya. Unlike these authors, who consider the group as a subgroup of Microdon, it here treated as a separate genus. This is done because of the phylogenetic results of Reemer and Ståhls (in press) and because it does not agree with the diagnosis of Microdon as defined in the present paper.

Ceratophya
Diversity and distribution. Described species: 4. Description of one additional species from Argentina is in preparation by the first author. Known from Central and South America (Panama to northern Argentina). Diagnosis. The combination of a complete transverse suture on the mesoscutum and a constricted abdomen is only found in Ceratrichomyia, Indascia Keiser, Indascia, 1958, Thompsodon gen. n. and certain species of Paramixogaster . Males are easily distinguished from all these taxa by the long pilosity of the basoflagellomere, and also by sternite 4, which is covered by the genital capsule. From Paramixogaster this genus also differs by the unfused tergites 3 and 4. Females are unknown.

Ceratrichomyia
Discussion. Séguy (1951) attributed one species to this genus. He designated a male and a female as 'types', and another male as 'cotype'. These are here all considered as syntypes. Examination of these three specimens made clear that they belong to three different species, which makes it necessary to designate a lectotype. The male with the following label data is here designated as lectotype. Label 1: "Madagascar, Behara"; label 2 (blue): "Museum Paris, III-38, A. Seyrig"; label 3 (red): "Type"; label 4: "Ceratrichomyia behara type du genre [male symbol] Séguy 50"; coll. MNHN. A redescription of the lecotype is given in the next section of the present paper. By this lectotype designation, the other two syntypes become paralectotypes. The male collected in Bekily (Madagascar) belongs to a new species of Ceratrichomyia, which is described in the present paper as C. bullabucca spec. n. The female paralectotype, collected in Bekily, is here considered to belong to a previously undescribed species of Paramixogaster, because it possesses all characters described as diagnostic for that genus (see genus account). A description of that species is given under the name Paramixogaster piptotus sp. n. A third species attributed to this genus, C. angolensis sp. n., is described from Angola.
The long pilosity of the male basoflagellomere was used by Séguy (1951) as a character to set his African genus Ceratrichomyia apart from other Microdontinae. This character is also present in Ptilobactrum Bezzi, 1915, another African taxon. Apparently Séguy was not aware of this, as he did not refer to Ptilobactrum. Cheng and Thompson (2008) did notice the similarity in antennal structure in both taxa and, based on the descriptions, proposed to regard Ceratrichomyia as a subjective junior synonym of Ptilobactrum.
Study of the type specimens of Ceratricomyia and Ptilobactrum revealed that these taxa are in fact very different. While Ceratrichomyia has, for instance, a constricted abdomen with unfused tergites 3 and 4, Ptilobactrum has a conical abdomen with fused tergites 3 and 4. The structures of the male genitalia are also very different (compare Figs 56-58 with 326), e.g. with a deeply furcate surstylus in Ceratrichomyia and an unfurcate one in Ptilobactrum. Considering these morphological differences, and supported by the phylogenetic results of Reemer and Ståhls (in press), Ceratrichomyia is here re-instated as a valid genus.
Diversity and distribution. Described species: 3. Two species are known from Madagascar, one from the African mainland (Angola). Discussion. Ceriomicrodon is treated as a subgenus of Microdon by Thompson et al. (1976) and Cheng and Thompson (2008). However, it does not agree with the diagnosis of Microdon as used in the present paper, because of several characters (e.g. postpronotum bare, abdomen petiolate, phallus with dorsal process long and whiplike). In addition, the phylogenetic results of Reemer and Ståhls (in press) indicate a relationship with e.g. Pseudomicrodon and Rhopalosyrphus.

Ceriomicrodon
Diversity and distribution.  Ferguson (1926a) argued that the furcate antenna provides insufficient basis for erecting a new genus for Microdon alcicornis,  decided to erect Cervicorniphora for this species, as a subgenus of Microdon. Cheng and Thompson (2008) also considered this genus-group as a subgenus of Microdon. The phylogenetic analysis of morphological characters by Reemer and Ståhls (in press) did not provide many clues as to the taxonomic affinities of this taxon, although it seems clear that it is not related to other taxa in which the male has a furcate basoflagellomere. As the characters of Cervicorniphora (e.g. phallus not furcate) do not fit in the concept of Microdon s.s. (phallus furcate near base) as defined in the current paper, Cervicorniphora is here raised to genus rank, to avoid disrupting the monophyly of Microdon.
The female is unknown. In most other microdontine taxa in which the male has a furcate basoflagellomere (e.g. Carreramyia, Schizoceratomyia), the female has an unfur-cate basoflagellomere. So, the possibility that the female of Cervicorniphora has unfurcate antennae should be taken into account.
Description. Body length: 8-10 mm. Metallic green to bluish flies (legs may be yellowish), entire body densely and coarsely punctate, mimics of Chrysididae (Hymenoptera). Head about as wide as thorax. Face convexly produced in profile; about as wide as an eye. Lateral oral margins produced. Vertex flat. Occiput ventrally narrow, dorsally strongly widened. Eye densely pilose. Eyes in male with mutual distance smaller than width of antennal fossa. Antennal fossa twice as wide as high, dorsally covered by 'shelf-like' extension of frons. Antenna longer than distance between antennal fossa and anterior oral margin; basoflagellomere longer than scape, oval; bare. Postpronotum pilose. Notal wing lamina strongly developed; partly overlapping membranes around wing insertion. Scutellum semicircular; with calcars. Anepisternum moderately sulcate; with bare part limited to ventral half. Anepimeron entirely pilose. Katepimeron flat; bare. Katatergum carinate. Wing: vein R4+5 with posterior appendix; vein M1 perpendicular to vein R4+5; postero-apical corner of cell r4+5 widely rounded; crossvein r-m located around basal 1/4 of cell dm. Abdomen oval, about 1.5 times as long as wide. Posterior margin of tergite 1 angular. Tergites 3 and 4 fused. Male genitalia: phallus unfurcate; epandrium without ventrolateral ridge; surstylus furcate, with anterior part short and wide, posterior process long and narrow. Diagnosis. Head, thorax and abdomen metallic green or blue. Antennal fossa twice as wide as high, dorsally covered by 'shelf-like' extension of frons.
Discussion. Chrysidimyia was treated as a synonym of Microdon by Thompson et al. (1976), but the unfurcate phallus and the phylogenetic results of Reemer and Ståhls (in press) indicate that this status cannot be maitained. Instead, the male genitalia of Chrysidimyia ( Fig. 65) resemble those of Laetodon (Fig. 135); these taxa share an unfurcate phallus and a long posterior process on the surstylus. These taxa also have their metallic body colouration and pilose eyes in common. These characters may suggest a phylogenetic relationship, although this is not found by Reemer and Ståhls (in press), who recovered Chrysidimyia in a large polytomy. Besides, the 'shelf-like' extension of the frons and dense punctuation of the body are not found in Laetodon. For this reason, we prefer to treat the groups separately.
Diversity and distribution. Described species: 1. One additional, undescribed species is known to the first author. All known records are from the Amazon region of South America, including the Guyana shield. Description. Body length: 6-8 mm. Moderately small flies with short antennae and oval abdomen. Head a little wider than thorax. Face convex; about as wide as or narrower than an eye. Lateral oral margins weakly produced. Vertex convexly produced, more or less shining, sparsely pilose, almost bare on anterior half. Occiput ventrally narrow, dorsally widened. Eye bare. Eye margins in male weakly converging at level of frons, with mutual distance 3-5 times width of antennal fossa. Antennal fossa about as wide as high. Antenna longer than distance between antennal fossa and anterior oral margin; basoflagellomere as long as or longer than scape, bare. Postpronotum pilose. Scutellum semicircular; with calcars. Anepisternum sulcate; pilose anterodorsally and posteriorly, widely bare in between. Anepimeron entirely pilose. Katepimeron almost flat to convex; often with wrinkled texture; bare. Wing: vein R4+5 with posterior appendix; vein M1 perpendicular to vein R4+5; postero-apical corner of cell r4+5 rectangular, with small appendix; crossvein r-m located between basal 1/6 to 1/4 of cell dm. Abdomen oval, about 1.5 to 2 times as long as wide. Tergites 3 and 4 fused. Sternite 1 bare. Male genitalia: phallus furcate near apex, with dorsal process long and whip-like, ventral process very short; epandrium with ventrolateral ridge.
Discussion. All species assigned to this genus were previously undescribed or are still undescribed.
The phylogenetic analysis based on morphology places the type species (D. zodiacus sp. n.) in the same clade as Omegasyrphus Giglio-Tos, 1891, Pseudomicrodon Hull, 1937 andRhopalosyrphus Giglio-Tos, 1891 (Reemer andStåhls in press). In addition to this phylogenetic evidence, the male genitalia of these taxa are all similar in the structure of the phallus and the shape of the surstylus. Because of the oval, non-constricted abdomen, Domodon species superficially may seem most similar to Omegasyrphus, but differ from that genus by the convex and sparsely pilose vertex, the long antenna, and the medially widely bare anepisternum. With Pseudomicrodon it shares the convex and sparsely pilose vertex, as well as the structure of the male genitalia, but Domodon differs from that genus by the oval (instead of constricted) abdomen. Instead of arbitrarily assigning the species in question to one of the mentioned genera, it is here considered preferable to erect a new genus, so as to emphasize the distinctive features of this group.
Diversity and distribution. Described species: 1. Surinam. Four additional, undescribed species are known by the first author from French Guyana, Surinam and Costa Rica. Probably the group is widespread in Central and South America.
Etymology. The generic name is a combination of domus and odon, with the latter used as a suffix derived from Microdon. The Latin word domus is here used in the meaning of 'dome' and refers to the convex (dome-shaped) vertex of the species in this genus. The name is to be treated as masculine. Diversity and distribution. Described species: 2. The type species was found in a mountainous area in southeastern China. The second known species, Furcantenna nepalensis sp. n., was collected in the Nepalese Himalaya at an altitude of approximately 1800 meters. The discovery of these species in these areas sheds an interesting light on the biogeography of the taxa with a furcate basoflagellomere in the male. Prior to the description of Furcantenna, such taxa were almost exclusively known from South America (except for the the apparently unrelated Australian Cervicorniphora). The occurrence of the obviously related (Reemer and Ståhls in press) Furcantenna in Oriental mountains on the Asian mainland could possibly be explained as a relict of a wider distribution in early eras. Description. Body length: 8-12 mm. Moderately slender to broadly built flies with long antennae; abdomen oval, slightly tapering or basally slightly constricted; often with fasciate patterns of golden pile on thorax and abdomen, sometimes with yellow abdominal markings. Head slightly wider or slightly narrower than thorax. Face convex; narrower than to as wide as an eye. Lateral oral margins produced. Vertex flat. Occiput ventrally narrow, dorsally widened. Eye short pilose or bare. Eye margins in male converging at level of frons, with mutual distance 1.5-2 times as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna about as long as distance between antennal fossa and anterior oral margin; basoflagellomere shorter than scape; bare. Postpronotum pilose. Scutellum semicircular; with calcars. Anepisternum sulcate; entirely pilose, except for small bare part ventrally. Anepimeron entirely pilose. Katepimeron convex or nearly flat; with or without wrinkled texture; bare or pilose. Wing: vein R4+5 with posterior appendix; vein M1 more or less straight, perpendicular to vein R4+5; postero-apical corner of cell r4+5 rounded or rectangular, with or without small appendix; crossvein r-m located between basal 1/6 and 1/5 of cell dm. Abdomen oval or basally constricted, 1.5-3 times as long as wide. Tergites 3 and 4 fused. Sternite 1 pilose. Male genitalia: phallus projecting little beyond apex of hypandrium, bent dorsad, furcate with furcation point from halfway to near apex, with both processes about equally long; epandrium without ventrolateral ridge; surstylus with subbasal excavation, dividing surstylus into a basal lamella and a long posterior process.
Discussion. All previously described species included in this genus were originally described in the genus Microdon. In the most recent catalogue of Oriental Microdontinae these species were listed under that genus (Knutson et al. 1975). As Microdon is defined more strictly in the present paper, the species can no longer be placed in that genus, hence a new genus is erected. Three new species are described in the present paper.
Diversity and distribution. Described species: 8. Oriental, ranging from Sri Lanka to Thailand, Vietnam, Java and Borneo.
Etymology. The generic name is composed of the Greek words helios (sun) and odon, with the latter part used as a suffix derived from Microdon. The first part was chosen to emphasize the Oriental ('where the sun rises') distribution of the genus.  Hull, 1937: 21, by original designation.
Description. Body length: 7-10 mm. Stingless bee mimicking flies with short to moderately long antennae and oval to triangular abdomen. Head slightly wider than thorax. Face convex; narrower than an eye. Lateral oral margins not produced. Vertex narrow, in most species convexly produced and shining, flat in some species. Occiput narrow over entire length, except ventrally strongly widened in H. ulopodus. Eye with short, sparse pile. Eye margins in male strongly converging at level of frons, with mutual distance smaller than width of antennal fossa, except 3 times as wide in H. ulopodus. Antennal fossa about as wide as high. Antenna as long as or shorter than distance between antennal fossa and anterior oral margin; basoflagellomere shorter to longer than scape, oval; bare. Postpronotum pilose. Scutellum semicircular, triangular or apicomedially sulcate; without calcars. Anepisternum without or with weak sulcus; pilose anterodorsally and posteriorly, widely bare in between. Anepimeron entirely pilose. Katepimeron convex; bare. Wing: vein R4+5 without posterior appendix; vein M1 perpendicular to vein R4+5; postero-apical corner of cell r4+5 rectangular, with small appendix; crossvein r-m located between basal 1/8 to 1/4 of cell dm. Abdomen oval or kite-shaped, 1.2 to 2 times as long as wide. Tergites 3 and 4 fused. Sternite 1 pilose. Male genitalia: phallus furcate near apex, with dorsal process in some species a little longer than ventral process; epandrium with or without ventrolateral ridge. Diagnosis. Vein R4+5 without posterior appendix. Crossvein r-m located between basal 1/8 and 1/4 of cell dm. Subcostal vein joins costal vein after level of crossvein r-m. Postpronotum pilose. Abdomen oval or kite-shaped (tergite 2 wide, subsequent tergites triangularly narrowing). Antenna as long as or shorter than distance between antennal fossa and anterior oral margin. Basoflagellomere not furcate. Occiput narrow in dorsal half (usually also in ventral half, except in H. ulopodus Hull, 1944).
Discussion. When Hull (1937a) erected the genus Hypselosyrphus for his species trigonus, he mentioned its similarity to Ubristes Walker, 1852 species, without clearly stating the differences. In his key to the groups of Microdontinae, Hull (1949) separated these taxa by the absence (Hypselosyrphus) or presence (Ubristes) of an appendix on vein R4+5. This character serves well to separate Hypselosyrphus from Ubristes s.s. as defined in the present paper, and almost always for Stipomorpha (appendix on vein R4+5 seldomly missing), which was included in Ubristes until now. In later keys and catalogues, Hypselosyrphus was treated as a junior synonym of Ubristes (Thompson 1969, Thompson et al. 1976). Cheng and Thompson (2008) also considered Hypselosyrphus (and Stipomorpha Hull, 1945) synonymous with Ubristes, but nevertheless differentiated the groups in their key. They consider abdominal shape to be diagnostic: oval or rectangular in Ubristes, short, almost equilaterally triangular in Hypselosyrphus, much longer, isosceles triangular in Stipomorpha. As there are many varieties in abdominal shape among the the taxa involved, it is hard to decide where to draw the line. Other characters are necessary to distinguish these taxa satisfyingly (see key and diagnoses).
Diversity and distribution. Described species: 11. Descriptions of five additional species are in preparation by the first author. Hypselosyrphus is known from Panama, the Amazon region and southern Brazil. Considering the small number of specimens known, it seems likely that the genus is widespread in tropical South America. Discussion. Originally this genus was included in the tribe Sphegini, as part of a subfamily Cheilosiinae (Keiser 1958). Thompson (1969) correctly recognized that it belongs to the Microdontinae, where it has remained since.

Indascia
Originally, Indascia was based on two species with short antennae and without a posterior appendix on vein R4+5 (Keiser 1958). In two of the species included in the phylogenetic analyses of Reemer and Ståhls (in press) the antennae are long and the appendix on vein R4+5 is present (Indascia gigantica sp. n. and I. spathulata sp. n.). Both characters are also found in additional undescribed species known to the first author. Therefore, these characters are considered not to be of diagnostic value for this genus.
Superficially, species of Indascia look similar to those of Paramicrodon de Meijere, 1913 (as noticed by Cheng and Thompson 2008). For discussion on similarities with Paramixogaster Brunetti, 1923 see there.
Diversity and distribution. Described species: 4. At least four undescribed species are known to the first author. The genus appears to be strictly Oriental, with species known from India, Sri Lanka, Pakistan, Thailand and Vietnam. The origin of the type specimens of the type species ('India orientalis') is not exactly known. Description. Body length: 12-14 mm. Large flies with long antennae (pilose in male) and oval abdomen, which may be constricted basally. Head wider than thorax. Face in profile more or less straight, ventrally produced below eye margin; wider than eye. Lateral oral margins weakly produced. Vertex strongly swollen. Occiput narrow ventrally, strongly widened dorsally. Eye bare. Eyes in male not converging at level of frons; mutual distance about 5 times width of antennal fossa. Antennal fossa about as high as wide. Antenna longer than height of head. Basoflagellomere 3.5-4 (male) or 2.5 (female) times as long as scape; with long pilosity in male, bare in female. Postpronotum pilose. Mesoscutum with transverse suture incomplete. Scutellum semicircular, without calcars. Anepisternum with deep sulcus; pilose anterodorsally and posteriorly, widely bare in between. Anepimeron entirely pilose. Katepimeron convex; with or without wrinkled texture; with rows of microtrichia. Wing: vein R4+5 with posterior appendix; vein M1 in anterior half with outward angle; postero-apical corner of cell r4+5 rectangular, with small appendix; crossvein r-m located between basal 1/6 and 1/5 of cell dm. Abdomen either oval or somewhat constricted at base, in the latter case with tergite 4 curved downward and more or less perpendicular to tergite 2. Tergites 3 and 4 not fused, able to articulate independently. In male K. pendulosa, sternite 4 is covered by the genital capsule and therefore not visible without removing genitalia, while the lateral margins of tergite 3 are strongly curved and 'tucked away' under sternite 3 (Fig. 123). Male genitalia: phallus slender, furcate near apex, basally complexly bent into curves, interconnected by a membrane; epandrium without ventrolateral ridge; surstylus approximately oval. Diagnosis. Vein R4+5 with posterior appendix. Postpronotum pilose. Propleuron bare. Mesonotal transverse suture incomplete. Tergites 3 and 4 not fused, able to articulate independently. Anepisternum widely bare of pile (but with microtrichia) medially, also on dorsal half. Male basoflagellomere with long pile.

Kryptopyga
Discussion. Hull (1944a) erected the genus and assigned one species to it: K. pendulosa Hull, 1944. He considered it close to the African genus Ptilobactrum Bezzi, 1915 because of the long pile on the basoflagellomere, but considered it distinct because of the subpetiolate abdomen and the remarkable structure of the 3rd and 4th abdominal segments. The pilose basoflagellomere in the male is also found in Ceratrichomyia, with which Kryptopyga also shares the swollen vertex and dorsal occiput, and the unfused tergites 3 and 4. The male genitalia, however, are quite different, and in Kryptopyga the mesonotal transverse suture is incomplete.
Together with the Nearctic Microdon craigheidi Walton, 1912, Kryptopyga is the only known taxon of Microdontinae in which the phallus is not simply curved between base and apex, but complexly bent into a couple of curves basally, interconnected by a membrane (compare Fig. 131 with Fig. 232). Despite this common character, there is no reason to suspect a closer relationship between these taxa.
The abdomen in K. pendulosa is much more modified than in K. sulawesiana sp. n., but the latter species is nevertheless regarded as belonging to the genus based on the pilose basoflagellomere, the shape of the head, the wing venation and the structure of the male genitalia, in which it is all very similar to K. pendulosa.
Microdon tuberculatus Shiraki, 1968 might also belong in Kryptopyga, because of its unfused tergites 3 and 4 and similarity in head shape (strongly swollen vertex and dorsal occiput, face ventrally produced below eye margin). However, only the female of this species is known, so it is unknown whether the male has long pile on the basoflagellomere and the characteristic genitalia of Kryptopyga. Therefore, this species is presently left unclassified. As de Meijere (1913) had already used the same species name, the replacement name shirakii is here proposed.
Diversity and distribution. Description. Body length: 6-9 mm. Small, metallic green to blue flies, with long antennae and oval abdomen. Head about as wide as thorax or slightly wider. Face convex; narrower than an eye. Lateral oral margins weakly produced. Vertex flat. Occiput ventrally narrow, dorsally widened. Eye pilose. Eye margins in male converging at level of frons, with mutual distance 2 to 4 times as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna about as long as to longer than distance between antennal fossa and anterior oral margin; basoflagellomere longer than scape, oval; bare. Postpronotum pilose. Scutellum semicircular; with calcars, which may be spatulate (widened and dorsoventrally flattened). Anepisternum weakly sulcate; pilose anteriorly and posteriorly, widely bare in between. Anepimeron entirely pilose. Katepimeron convex; smooth; bare. Wing: vein R4+5 with posterior appendix; vein M1 perpendicular to vein R4+5; postero-apical corner of cell r4+5 rectangular, with small appendix; crossvein r-m located between basal 1/6 to 1/5 of cell dm. Abdomen oval, about 1.5 to 2 times as long as wide. Tergites 3 and 4 fused. Sternite 1 pilose or bare. Male genitalia: phallus unfurcate, projecting slightly beyond apex of hypandrium; hypandrium with basal part bulb-like; epandrium without ventrolateral ridge; surstylus shallowly furcate, with long posterior process.
Discussion. The species included in this genus used to be placed in Microdon (Thompson 1981b). Morphology of the male genitalia, however, is quite distinct from that of Microdon as defined in the present paper: the phallus is short and unfurcate, the epandrium lacks the ventrolateral ridge. Based on these morphological differences and the phylogenetic results of Reemer and Ståhls (in press), Laetodon is here erected as a new genus. See Chrysidimyia for discussion on possible relationships with that genus.
Etymology. The generic name is composed of laetus and odon, with the first part derived from Microdon laetus Loew, 1864 (the type species of the genus), and the latter used as a suffix derived from Microdon. Description. Body length: 4-7 mm. Small, delicate flies with long antennae and flat abdomen. Head slightly to much wider than thorax. Face concave, either entirely or only laterally; wider than an eye. Mouth parts undeveloped: oral opening absent or hardly visible. Vertex more or less flat, not strongly produced or convex. Occiput ventrally narrow or widened, dorsally widened. Eye bare. Eyes in male not converging at level of frons, with mutual distance about 4 times the width of antennal fossa. Antennal fossa about as wide as high or about 1.5 times as wide as high. Antenna as long as or longer than distance between antennal fossa and anterior oral margin; basoflagellomere longer than scape, multifurcate in male (3 to 14 branches), unfurcate in female; bare; arista absent in male, present in female. Postpronotum bare. Scutellum semicircular; without calcars. Anepisternum convex; entirely with sparse, bristle-like pile. Anepimeron bare or pilose. Katepimeron convex; bare; with or without wrinkled texture. Wing: vein R4+5 without posterior appendix; vein M1 perpendicular to vein R4+5; postero-apical corner of cell r4+5 widely rounded or rectangular, with or without small appendix; crossvein r-m located very close to base of cell dm (within basal 1/10). Abdomen dorsoventrally flattened; more or less trapezoid, with lateral margins gradually widening posteriad, with largest width at tergite 4; 1.5-2.5 times as long as wide. Tergites 3 and 4 fused. Male genitalia: phallus furcate near apex, straight, projecting not or hardly beyond apex of hypandrium; epandrium without ventrolateral ridge; surstylus unfurcate, more or less oval. Diagnosis. Vein R4+5 without posterior appendix. Postpronotum bare. Antenna at least as long as distance between antennal fossa and anterior oral margin. Antenna inserted on head above dorsal eye margin.

Masarygus
Discussion. Originally, this genus was erected as the first known member of a new family, the Masarygidae (Brèthes 1908;but journal publication was 1909but journal publication was , see Sabrosky 1999. Brèthes associated it with Conopidae and Scenopinidae because of the wing venation, and with Oestridae because of the reduced mouthparts. He also noted a superficial resemblance to certain Stratiomyidae. Bezzi (1910) was the first to recognize Masarygus as belonging to the Syrphidae and related to Microdon, by pointing out its resemblance to Ceratophya and the apparent relationship with ants (as noted by Brèthes 1908). Shannon (1925) considered Masarygus as a synonym of Microdon. Brèthes (1928) objected by pointing out that Masarygus differs from Microdon in the distinct sexual dimorphism and also in wing venation. All subsequent authors have included Masarygus in the Microdontinae.
Masarygus was the first described syrphid taxon with a furcate basoflagellomere (in the male sex only). A few other taxa with this character were described during the 20th century: Schizoceratomyia Carrera, Lopes & Lane, 1947, Johnsoniodon Curran, 1947and Carreramyia Doesburg, 1966. Masarygus, Schizoceratromyia and Johnsoniodon were considered synonymous by Hull (1949), who also regarded "Masarygus as a Rhoga with fissicorn antennae", without explicitly including all of these taxa in Rhoga (the oldest name). Papavero (1962) also considered Masarygus, Schizoceratomyia and Johnsoniodon synonymous, because he found that the number of branches on the basoflagellomere (four in Masarygus planifrons, two in the other taxa) was a species-level character rather than a generic character. Van Doesburg (1966) did not agree and considered Masarygus and Schizoceratomyia (including Johnsoniodon) as distinct genera, because of distinct differences in shape of head, antenna and abdomen. Thompson et al. (1976) followed the opinion of Papavero (1962). Cheng and Thompson (2008) considered Masarygus and Schizoceratomyia as distinct groups.
Masarygus palmipalpus sp. n. is considered related to M. planifrons because of the following shared characters: male basoflagellomere multifurcate; base of antenna in lateral view placed above dorsal eye margin; head strongly flattened; face concave; oral opening absent; abdomen dorsoventrally flattened; gradually widening hindward, with widest point at tergite 4; phallus furcate near apex, with both processes equally long.
In addition to Masarygus planifrons and M. palmipalpus, two undescribed species are considered to belong to this genus. These species are included in the phylogenetic analyses of Reemer and Ståhls (in press) under the names Masarygus sp. 1 and sp. 2. The latter has three branches on the basoflagellomere, the first approximately 14. Whereas sp. 1 is placed in the same clade as M. planifrons and M. palmipalpus by Reemer and Ståhls (in press) (based on adult morphology), sp. 2 is placed in the clade containing Schizoceratomyia and Carreramyia. Species 2 is nevertheless included in Masarygus, because of the following characters: basoflagellomere multifurcate and bare (instead of bifurcate and pilose as in Schizoceratomyia); arista absent (present in Schizoceratomyia); base of antenna inserted on head above dorsal eye margin (not below as in Schizoceratomyia); vertex not strongly produced (in contrast with Carreramyia); crossvein r-m located within basal 1/10 of cell dm (between basal 1/4 and 1/8 in Schizoceratomyia); hind tibia not swollen and without long, brush-like pile (in contrast with Carreramyia). Unfortunately, the genitalia of the only known specimen of Masarygus species 2 are lost: there is a microvial containing postabdominal segments attached to the pin, but there are no genitalia in it.
Diversity and distribution. Described species: 2. Neotropical. At least two undescribed species are known to occur (see Discussion). All species known so far, including the undescribed ones, have only been collected on one occasion. Description. Body length: 5-10 mm. Small, broadly built flies with long antennae and short, almost round abdomen. Head about as wide as thorax. Face convex; slighly narrower to slightly wider than an eye. Lateral oral margins not produced. Vertex flat. Occiput ventrally narrow, dorsally widened. Eye bare. Eye margins in male parallel, not converging at level of frons, with mutual distance 4 times as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna longer than distance between antennal fossa and anterior oral margin; basoflagellomere longer than scape, sickle-shaped; bare. Postpronotum pilose. Scutellum semicircular; with small calcars or only with pair of small tufts of black microtrichiae posteriorly. Anepisternum without sulcus; pilose on slightly less than dorsal half, bare on slightly more than ventral half. Anepimeron entirely pilose. Katepimeron convex; bare. Wing: vein R4+5 with posterior appendix; vein M1 perpendicular to vein R4+5; postero-apical corner of cell r4+5 rectangular, with small appendix; crossvein r-m located between basal 1/8 and 1/10 of cell dm. Abdomen approximately round, 1 to 1.2 times as long as wide. Tergites 3 and 4 fused. Sternite 1 bare. Male genitalia: phallus straight, furcate near apex, with both processes about equally long; hypandrium without apical part; epandrium without ventrolateral ridge; surstylus furcate, with anterior lobe small and narrow, posterior lobe larger and wider.
Discussion. This is the only one known taxon among the Microdontinae in which the apical part of the hypandrium is entirely lacking (Fig. 156). Among the Neotropical taxa, this taxon is unique in the sickle-shaped basoflagellomere. The latter character also occurs to some extent in some Nearctic (Microdon adventitus, M. globosus) and Old World taxa (some Archimicrodon, Myiacerapis, Oligeriops Hul, 1937), but these differ from Menidon in several other important characters, such as a furcate phallus (unfurcate in Oligeriops) and absence of apical part of hypandrium (present in all other Microdontinae). These morphological singularities, combined with the phylogenetic results of Reemer and Ståhls (in press) (sister of (Piruwa + Paramicrodon)), are reasons to place Microdon falcatus in its own genus. Thompson (2007) clarified the taxonomy of the type species, which has several synonyms.
Diversity and distribution. Described species: 1. Central and South America. Unpublished molecular evidence suggests that more than one species is involved, but this needs further study.
Etymology. The generic name is a combination of the Greek words mene (moon) and odon, with the latter used as a suffix derived from Microdon. The prefix meni-was chosen because of the crescent-shaped basoflagellomere in the type species. Type species: Mermerizon inbio spec. n. Type locality: Costa Rica.

Mermerizon
Description. Stingless bee mimicking flies with moderately long antennae and elongate oval abdomen. Head slightly wider than thorax. Face convex; narrower than an eye. Lateral oral margins not produced. Vertex flat. Occiput ventrally narrow, dorsally widened. Eye bare. Eye margins in male parallel, not converging at level of frons, with mutual distance 3-4 times as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna shorter than (may be almost as long as) distance between antennal fossa and anterior oral margin; basoflagellomere slightly shorter to longer than scape, oval; bare. Postpronotum pilose. Scutellum semicircular; without calcars. Anepisternum without sulcus; pilose on dorsal half, bare on ventral half. Anepimeron pilose on dorsal half, bare on ventral half. Katepimeron convex; bare. Wing: vein R4+5 with posterior appendix; vein M1 perpendicular to vein R4+5; postero-apical corner of cell r4+5 rectangular, with small appendix; crossvein r-m located around basal 1/10 of cell dm. Abdomen oval, 2 to 3 times as long as wide. Tergites 3 and 4 fused. Sternite 1 pilose. Male genitalia: phallus slightly bent dorsad, furcate near apex, with dorsal process at least twice as long as ventral process; hypandrium with bulb-like base; epandrium without ventrolateral ridge.
Discussion. The species of this genus are obvious mimics of stingless, Trigona-like bees in their tawny colouration and long pilose hind tibiae. At first sight they may be confused with Hypselosyrphus, Rhoga, or Stipomorhpa. From the first two genera, Mermerizon can be distinguished by the presence of a posterior appendix on vein R4+5, from Stipomorpha by the absence of a wide membrane between sternites 2 and 3. A presently undescribed Argentinian species lacks the long pilosity of the hind tibiae and does not seem to mimic these bees. Instead, it resembles Paragodon Thompson, 1969 andSurimyia Reemer, 2008 in general habitus, but is easily told apart by the presence of a posterior appendix on vein R4+5 and the male genitalia, which are very similar to those of the other two Mermerizon species.
Diversity and distribution. Described species: 1. Descriptions of two additional species are in preparation by the first author. Neotropical (presently known from Costa Rica and Argentina).
Etymology. The generic name is derived from the ancient Greek verb mermerizo, meaning 'to deliberate' or 'to ponder'. This name was chosen because it took some deliberation before making the decision that a new genus was to be erected for the involved species. The name is to be treated as masculine. Description. Body length: 7-21 mm. Slender to moderately broadly built flies with oval abdomen and long antennae. Head slightly wider than thorax. Face almost straight to convex in profile; narrower to wider than an eye. Lateral oral margins produced or not produced. Vertex flat. Occiput ventrally narrow, dorsally widened. Eye bare. Eye margins in male converging at level of frons, with mutual distance 2-3 times as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna longer than distance between antennal fossa and anterior oral margin; basoflagellomere shorter than scape; bare. Postpronotum pilose. Scutellum semicircular; with or without calcars. Anepisternum sulcate; entirely pilose, except sometimes with small bare part ventrally (only known exception: M. bifasciatus, in which anepisternum is bare on entire ventral half). Anepimeron entirely pilose. Katepimeron flat to somewhat convex; smooth or with wrinkled texture; not pilose, but often with rows of microtrichia. Katatergum with oblique rows of microtrichia. Wing: vein R4+5 with posterior appendix; vein M1 more or less straight, perpendicular to vein R4+5; postero-apical corner of cell r4+5 angular to widely rounded, with or without appendix; crossvein r-m located between basal 1/7 and 1/4 of cell dm. Abdomen oval, 1.5-2.5 times as long as wide. Tergites 3 and 4 fused. Sternite 1 pilose. Male genitalia: phallus projecting not or little beyond apex of hypandrium (except projecting well beyond apex of hypandrium in M. bifasciatus), bent dorsad, furcate in apical half, with both processes about equally long (except ventral process much longer in M. bifasciatus); epandrium with or without ventrolateral ridge; surstylus unfurcate, sometimes with long posterior process.

Metadon
Diagnosis. Body never metallic green or blue. Vein R4+5 with posterior appendix. Abdomen oval, longer than wide but less than 2.5 times as long as wide. Postpronotum pilose. Anepisternum with bare part limited to ventral half, or entirely pilose. Antenna longer than distance between antennal fossa and anterior oral margin. Basoflagellomere shorter than or as long as scape. Tergite 1 short: length/width ratio 1:25 or less.
Discussion. All included species (except the ones here described) were originally described in the genus Microdon. However, the morphology of Metadon is distinct. Characters that separate these taxa in all examined species (except M. bifasciatus, see below) are: anepisternum (almost) entirely pilose; phallus projecting not or only little beyond apex of hypandrium; aedegus furcate in apical half. Additional characters for distinguishing Metadon from Microdon (that may not work for all species) are: katepimeron more or less flat, with wrinkled texture; katatergum with oblique rows of microtrichia. In general, the abdomen of Metadon species is more elongate than that of Microdon species.
The East Palaearctic species M. bifasciatus Matsumura, 1916 is aberrant in certain characters. In this species the bare part of the anepisternum reaches up to about half the height of the sclerite. In addition, the genitalia are aberrant as the ventral aedeagal process is much longer than the dorsal process (Fig. 172), a character not known from any other species of Microdontinae. Nevertheless, this species is placed in Metadon because of the elongate abdomen and the oblique rows of microtrichia on the katatergum. This is supported by the results of Reemer and Ståhls (in press). As the Chinese species Microdon brunneipennis Huo, Ren & Zheng, 2007and M. pingliensis Huo, Ren & Zheng, 2007and M. spuribifasciatus Huo, Ren & Zheng, 2007 are similar to M. bifasciatus, the characters as mentioned may also be valid for those species.
Metadon is erected as a new genus distinct from Microdon in order to facilitate distinction between these apparently monophyletic groups. Results of phylogenetic analyses by Reemer and Ståhls (in press) support this decision.
Diversity and distribution. Described species: 42. About half of the species (22) are described from the Oriental region. Several undescribed species from this region were seen by the first author in different collections. From the Afrotropical region, 14 species are described, remarkably none of which is from Madagascar. Four species are known from the Palaearctic region. These seem to form a closely related species group, all related to M. bifasciatus, restricted to eastern China, Korea and Japan. Two species are known from the Aru Islands off the southwest coast of New Guinea (these were collected by Alfred Russel Wallace in 1857, to be described by Walker 1858). These are the only known records of this group from the Australian region.
Etymology. The generic name is a combination of the ancient Greek words meta and odon, with the latter used as a suffix derived from Microdon. The prefix meta is used in the sense of 'near' or 'close', in order to indicate the resemblance in habitus to Microdon s.s. It is a masculine name.  Ferguson, 1926 Microdon carbonarius  Microdon macquariensis Ferguson, 1926 Microdon nigromarginalis Curran & Bryan, 1926 Microdon pagdeni Curran, 1942 Microdon pictipennis (Macquart, 1850) Microdon rieki Paramonov, 1957 Microdon trimacula Curran, 1928 Microdon tsara Keiser, 1971 Microdon unicolor Brunetti, 1915 Microdon waterhousei Ferguson, 1926 Subgenus Description. Body length: 10-16 mm. Broadly built flies with oval to round abdomen and long antennae. Head about as wide as to slightly narrower than thorax. Face convex in profile; slightly narrower to slightly wider than an eye. Lateral oral margins produced. Vertex flat. Occiput ventrally narrow, dorsally widened. Eye bare or very short pilose. Eye margins in male converging at level of frons, with mutual distance 1-3 times as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna longer than distance between antennal fossa and anterior oral margin; basoflagellomere shorter than scape; bare. Postpronotum pilose. Scutellum trapezoid; with calcars. Propleuron pilose. Anepisternum with sulcus; pilose anterodorsally and posteriorly, extensively bare ventrally and medially. Anepimeron entirely pilose. Katepimeron convex; smooth; bare. Katatergum uniformly microtrichose. Wing: vein R4+5 with posterior appendix; vein M1 with outward angle, often with outward appendix, anteriorly recurrent; postero-apical corner of cell r4+5 widely rounded, with or without appendix; crossvein r-m located between basal 1/5 and 1/3 of cell dm. Abdomen oval, 1-1.5 times as long as wide. Tergites 3 and 4 fused. Sternite 1 pilose. Male genitalia: phallus projecting far beyond apex of hypandrium, bent dorsad, furcate basally, with both processes equally long and very slender; epandrium with ventrolateral ridge; surstylus with two wide lobes; subepandrial sclerite with elongate anterior projection projecting well beyond surstylus in lateral view.

Microdon Meigen
Diagnosis. Vein R4+5 with posterior appendix. Abdomen oval. Vein M1 of characteristic shape: with outward angle, usually with small outward appendix, anteriorly recurrent ( Fig. 177). In addition to this character, this subgenus also differs from Microdon s.s. in the aedeagal processes being longer and more slender, and in the subepandrial sclerite projecting anteriorly well beyond the surstylus in lateral view ( Fig. 178-180).
Discussion. Species of this group are similar in overall habitus to Microdon s.s. Many species have metallic colours, but some are dull black or have a 'tiger-striped' abdomen. Previously, this group was considered to be exclusively Neotropical (Cheng and Thompson 2008). However, several Oriental and one Japanese species are very similar to the Neotropical species in both external characters and morphology of the male genitalia.
Diversity and distribution. Described species: 34. Neotropical (25 species), Oriental (7 species), Nearctic (1 species) and Eastern Palaearctic (1 species from southern Japan). Description. Body length: 8-12 mm. Broadly built flies with oval to round abdomen and long antennae. Head narrower than to about as wide as thorax. Face convex in profile; narrower to wider than an eye. Lateral oral margins not produced. Vertex flat. Occiput ventrally narrow, dorsally widened or narrow (only in M. abditus Thompson, 1981). Eye bare. Eye margins in male converging at level of frons, sometimes only weakly so (M. adventitius Thompson, 1981, M. fuscipennis (Macquart, 1834)) with mutual distance 2-5 times as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna longer than or as long as distance between antennal fossa and anterior oral margin; basoflagellomere shorter to longer than scape; bare. Postpronotum pilose. Scutellum semicircular to trapezoid; without calcars, but large and blunt calcars may seem to be present due to strong apicomedian sulcus. Propleuron bare. Anepisternum without sulcus (or only a very weak one dorsally); pilose dorsally, extensively bare on slightly more or slighly less than ventral half. Anepimeron entirely pilose. Katepimeron more or less convex; smooth or with wrinkled texture (M. fuscipennis); bare. Katatergum uniformly microtrichose. Wing: vein R4+5 with posterior appendix; vein M1 more or less straight, perpendicular to vein R4+5, slightly recurrent; posteroapical corner of cell r4+5 rectangular, with appendix; crossvein r-m located between basal 1/7 and 1/4 of cell dm. Abdomen oval, 1-1.5 times as long as wide. Tergites 3 and 4 fused. Sternite 1 pilose or bare. Male genitalia: phallus projecting little beyond apex of hypandrium, bent dorsad, furcate apically, with both processes equally long; epandrium with ventrolateral ridge; surstylus with wide basal lobe and narrow posterior lobe. Diagnosis. Difficult to diagnose, because included species vary strongly in several key characters. See key and discussion.

Subgenus Dimeraspis Newman
Discussion. This group was erected for the Nearctic Dimeraspis podagra Newman, 1838, a subjective synonym of Mulio globosus Fabricius, 1805 (Thompson 1981b). This species differs from Microdon s.s. in the unsulcate anepisternum, the bare propleuron, the rectangular postero-apical corner of cell r4+5, and the male genitalia: phallus apically furcate, hypandrium with bulb-like base. Some other Nearctic (and one Cuban) species are very similar in morphology of the male genitalia: M. abditus Thompson, 1981, M. adventitius Thompson, 1981 fuscipennis (Macquart, 1834), M. marmoratus Bigot, 1883, and M. remotus Knab, 1917. Thompson (1981b also regarded these species as related, with the 'globosus complex' (M. abditus, M. globosus, M. marmoratus) as sister to the fuscipennis-group (M. adventitius, M. fuscipennis, M. remotus). These species are also similar in their overall brownish colouration and in the wing venation. The morphological similarities are here taken as a reason to include all species in Dimeraspis. Because of similarities in male genitalia this group might tentatively be considered related to Archimicrodon, Menidon or Serichlamys. However, because of considerable uncertainty, the group is here treated as a subgenus of Microdon.
Mesophila Walker, 1849 was erected for Ceratophya fuscipennis Macquart. As this species is here included in the older genus group Dimeraspis, Mesophila becomes a junior synonym of Dimeraspis.

Subgenus Megodon Keiser
Description. Body length: 8-13 mm. Broadly built flies with oval abdomen and long antennae. Head about as wide as thorax. Face convex in profile; narrower than an eye. Lateral oral margins slightly produced. Vertex flat. Occiput narrow and parallelsided over entire length. Eye bare. Eye margins in male converging at level of frons, with mutual distance about equal to width of antennal fossa. Antennal fossa about as wide as high. Antenna longer than distance between antennal fossa and anterior oral margin; basoflagellomere shorter than to as long as scape; bare. Postpronotum pilose. Scutellum trapezoid; with strongly developed calcars. Anepisternum weakly sulcate; pilose anterodorsally and along posterior margin, widely bare in between. Anepimeron entirely pilose. Katepimeron convex; smooth; bare. Wing: vein R4+5 with posterior appendix; vein M1 more or less straight, perpendicular to vein R4+5; postero-apical corner of cell r4+5 angular to weakly rounded, with or without appendix; crossvein r-m located around basal 1/6 of cell dm. Abdomen oval, around 1.5 times as long as wide. Tergites 3 and 4 fused. Sternite 1 pilose or bare. Male genitalia: phallus furcate near base, with processes equally long and projecting well beyond apex of hypandrium; epandrium with ventrolateral ridge; surstylus unfurcate, elongate, curved dorsad. Diagnosis. Vein R4+5 with posterior appendix. Postpronotum pilose. Abdomen oval. Anepisternum widely bare medially. Propleuron bare. Postero-apical corner of cell r4+5 more or less rectangular. Antenna longer than distance between antennal fossa and anterior oral margin. Occiput narrow and parallel-sided over entire length (not widened dorsally). First tarsomere of hind leg dorsally with wide longitudinal groove.
Discussion. Keiser (1971) erected this genus to include a species with very large, cone-shaped scutellar calcars. Cheng and Thompson (2008) did not study this species and refrained from commenting on the status of the group. The first author was able to study the holotype of Megodon stuckenbergi Keiser, 1971, as well as some additional material.
Megodon is very similar in external morphology to Microdon. Their genitalia also share important characters, like the deeply furcate phallus, the long aedeagal processes and the presence of a ventrolateral ridge on the epandrium. There are also differences, most notably the entirely narrow and parallel-sided occiput, and the dorsal, longitudinal groove on the first tarsomere of the hind leg. The shared characters are here considered more important than the differences. Because of these considerations, combined with the phylogenetic results of Reemer and Ståhls (in press), Megodon is here treated as a subgenus of Microdon.
Microdon planitarsus Keiser, 1971 is here also assigned to Megodon, because it agrees with the diagnostic characters as described above, and its male genitalia are very similar to those of M. stuckenbergi (Figs 193,195). In M. planitarsis, the scutellar calcars are not as large and cone-shaped as in M. stuckenbergi. This indicates that the size and shape of these calcars should not be regarded as group-defining.
Diversity and distribution. Described species: 2. Madagascar. One undescribed species from Madagascar is known to the first author.

Subgenus Microdon Meigen s.s. Figs 196-214
Description. Body length: 7-14 mm. Broadly built flies with oval abdomen and long antennae. Head narrower to slightly wider than thorax. Face convex in profile; slightly narrower to wider than an eye. Lateral oral margins not or weakly produced. Vertex flat. Occiput ventrally narrow to wide, dorsally widened. Eye bare. Eye margins in male converging at level of frons, with mutual distance 2-4 times as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna longer than distance between antennal fossa and anterior oral margin; basoflagellomere shorter to longer than scape; bare. Postpronotum pilose. Scutellum semicircular to trapezoid; with or without calcars. Propleuron pilose. Anepisternum sulcate; pilose anterodorsally and posteriorly, widely bare ventrally and medially. Anepimeron entirely pilose. Katepimeron convex; smooth; bare. Katatergum uniformly microtrichose. Wing: vein R4+5 with posterior appendix; vein M1 more or less straight, perpendicular to vein R4+5, sometimes with slight inward angle in anterior 1/3; postero-apical corner of cell r4+5 rounded, with or without appendix; crossvein r-m located between basal 1/6 and 1/4 of cell dm. Abdomen oval, 1-1.5 times as long as wide. Tergites 3 and 4 fused. Sternite 1 pilose. Male genitalia: phallus projecting clearly beyond apex of hypandrium, bent dorsad, furcate close to base, with both processes about equally long or dorsal process longer than ventral process; epandrium with ventrolateral ridge; surstylus with two short, wide lobes.
Discussion. As Cheng and Thompson (2008) wrote, this genus has remained "somewhat a catch all for various unrelated species not placed in other genera". Many species previously placed in Microdon are transferred to other genera in the present paper, e.g. Archimicrodon, Metadon and Peradon. These classificatory changes are supported by the results of the phylogenetic analysis of combined molecular and morphological characters by Reemer and Ståhls (in press). The analysis of only morphological characters by Reemer and Ståhls (in press) included many additional species which do not obviously belong to any of the previously recognized genus groups, nor to the genera erected in the present paper. The phylogenetic results offer little or no clues as to their taxonomic affinities. As most of these species were originally described in Microdon, and were subsequently maintained in that genus, the pragmatic solution is here chosen to keep these taxa in Microdon s.l. (see below). This category should not be confused with the supposedly monophyletic Microdon s.s. as defined above, as Microdon s.l. is probably not monophyletic. For some of these taxa, genus group names are available, which are here treated as subgenera (see separate accounts). The other taxa are here placed in species groups or left unplaced. These taxa are discussed below.
Unlike the other species groups discussed below, the virgo species group is considered to belong within Microdon s.s.
Description. Body length: 12 mm. Broadly built flies with bee-like pilosity and long antennae. Head wider than thorax. Face convex; wider than an eye. Lateral oral mar-gins not produced. Vertex flat. Occiput ventrally narrow, dorsally widened. Eye bare or very short and sparsely pilose. Eye margins in male hardly converging at level of frons, with mutual distance about 5 times as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna longer than distance between antennal fossa and anterior oral margin; basoflagellomere longer than scape; bare. Postpronotum pilose. Scutellum semicircular; without calcars. Anepisternum weakly sulcate; pilose anteriorly and posteriorly, widely bare in between. Anepimeron entirely pilose. Katepimeron convex; with wrinkled texture; bare. Wing: vein R4+5 with posterior appendix; vein M1 slightly recurrent, but more or less perpendicular to vein R4+5; postero-apical corner of cell r4+5 rounded, without appendix; crossvein r-m located around basal 1/4 of cell dm. Abdomen oval, about 1.5 times as long as wide. Tergites 3 and 4 fused. Sternite 1 pilose. Male genitalia: phallus furcate, with furcation point near base; epandrium with ventrolateral ridge; surstylus unfurcate.
Discussion. Myiacerapis was described as a subgenus of Microdon. In morphology it is quite similar to Microdon s.s. as defined in the present paper, also in the male genitalia (deeply furcate phallus with equally long processes, epandrium with ventrolateral ridge). However, unlike Microdon s.s. it has a bare proepimeron (pilose in Microdon s.s.) and a wrinkled texture of the katepimeron. Therefore, it is not placed in Microdon s.s. here, but in Microdon s.l, in awaitance of better understanding of its phylogenetic affinities.
Diversity and distribution. Described species: 1. Africa (Uganda). An undescribed species is known from South Africa (coll. BMNH).
Description. Body length: 25-28 mm. Very large flies with oval abdomen and long, colourful pilosity. Mimics of orchid bees of the genus Eulaema (Euglossidae). Head about as wide as thorax. Face more or less straight in profile; narrower than an eye; on ventral half with very long, thick and dense pile, resembling a beard ('mystax'). Eye margins in male converging at level of frons, with mutual distance about twice as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna longer than distance between antennal fossa and anterior oral margin; basoflagellomere shorter than scape, oval, about four times as long as wide, bare. Postpronotum bare. Scutellum trapezoid; with very large, cone-shaped calcars. Anepisternum sulcate; pilose anterodorsally and posteriorly, widely bare medially. Anepimeron entirely pilose. Katepimeron convex; smooth; bare. Wing: vein R4+5 with posterior appendix; vein M1 straight, perpendicular to vein R4+5; postero-apical corner of cell r4+5 widely rounded, without appendix; crossvein r-m located around basal 2/7 of cell dm. Abdomen oval, about 1.3 times as long as wide. Tergites 3 and 4 fused. Sternite 1 pilose. Male genitalia: phallus furcate, with furcation point near base, both processes about equally long, curved dorsad, projecting well beyond apex of hypandrium; epandrium without ventrolateral ridge; surstylus shallowly furcate, with two short and wide lobes. Diagnosis. Body length more than 20 mm. Face with very long, thick and dense pile, resembling a beard ('mystax').
Discussion. Hull (1937b) erected Syrphipogon, and considered it related to Microdon. Steyskal (1953) referred to Hull's description in his own description of an apparently very similar species (Microdon gaigei Steyskal, 1953), but he considered the differences with Microdon insufficient for generic status. In external characters and male genitalia Microdon and Syrphipogon are quite similar. For that reason, Syrphipogon is here still treated as a subgenus of Microdon.
The differences between the two species of Syrphipogon are not very convincing when comparing the description of Steyskal (1953), based on a female, with the holotype of S. fucatissimus Hull, 1937, a male. The differences as noted by Steyskal (1953) may be due to sexual dimorphism, but in order to establish this, the type of Microdon gaigei needs to be examined.
Diversity and distribution. Described species: 2. Neotropical. Only two specimens are known: one from Panama and one from "South America".

Microdon s.l. (species groups and unplaced species)
craigheadii-group. Only one species is included in this group: Microdon craigheadii Walton, 1912. This slender, metallic green Nearctic species is similar in habitus to Laetodon and many species of Microdon s.l. From these groups, M. craigheadii differs in the structure of the basal part of the phallus: the part of the phallus connecting the basal spherical part with the apical part is complexly curved (Fig. 232). This is a very unusual structure in Microdontinae, only found in this species and in Kryptopyga. In other genitalic structures (phallus deeply furcate, epandrium with ventrolateral ridge) as well in external morphology, M. craigheadii is very similar to Microdon s.s. Because of the peculiar morphology of the genitalia, the species is placed in a separate species group within Microdon s.l. erythros-group. In overall habitus and many external characters, the species of this group remind of both Microdon s.s. and Metadon. Placement in Microdon s.s. is contradicted by the phallus being furcate apically (Fig. 233), whereas placement in Metadon is contradicted by the extensively bare anepisternum. As the phylogenetic analysis of morphological characters (Reemer and Ståhls in press) provides no information on the affinities of Microdon erythros Bezzi, 1908, this species is placed in Microdon s.l., along with the similar M. luteiventris Bezzi, 1915. mirabilis-group. The species of this Neotropical group have contrasting yellow and black colour patterns on the wings, combined with remarkably long hind legs, evoking a resemblance to certain Pompilidae (Hymenoptera). Apart from this, they differ from Microdon s.s. in the bare propleuron and the aedeagal processes projecting hardly beyond the apex of the hypandrium.
Apart from Microdon mirabilis, this group includes M. bertonii Bezzi, 1910(= M. arcuatus Curran, 1941, syn. n.) and M. iheringi Bezzi, 1910. The species seem to differ only in colouration of wings, legs and abdomen. However, quick glances in museum collections (e.g. USNM) suggest that intermediate specimens exist. This indicates that species taxonomy of this group needs further attention. Bezzi (1910) wrote that he had two male specimens Microdon iheringi in his collection, which he both considered as 'cotypes'. The collection of the MCSN (Milan) presently holds only one specimen (a male), which was examined by the first author. It is uncertain whether the other specimen still exists. In order to assure stability of this taxon, the specimen in the MCSN-collection is here designated as lectotype. Label information is as follows: label 1: "5695"; label 2: "S. Paulo / Brasile / 26.X.06 / Hering"; label 3: "iheringi"; label 4 (red): "LECTOTYPE / Microdon iheringi / Bezzi, 1910/ Des. M. Reemer 2009 tarsalis-group. This group only includes the Afrotropical species Microdon tarsalis Hervé-Bazin, 1913 and its synonym Microdon bequaerti Curran, 1929 (syn. n.). In the phylogenetic analysis of morphological characters (Reemer and Ståhls in press) this species was recovered in the Microdon s.l. clade, but its exact relationship with the other groups in this clade were unresolved. This group differs from Microdon s.l. in e.g. the entirely narrow occiput, the short and characteristically shaped phallus with the dorsal process longer than the ventral process, and the absence of a ventrolateral ridge on the epandrium. Besides, there is a patch of pile with hook-shaped apexes on the hind basitarsus dorsally on its inner surface.
In overall habitus (including swollen hind basitarsus), M. tarsalis is remarkably similar to the Nearctic Microdon (Dimeraspis) abditus Thompson, 1981 but considering the differences in male genitalia this similarity is probably merely superficial. These differences are: phallus with dorsal process longer than ventral process (equally long in M. abditus), epandrium without ventrolateral ridge (with ventrolateral ridge in M. abditus), surstylus simple shaped, without distinct posterior process (with posterior process in M. abditus).
virgo-group. This group consists of Neotropical metallic green, blue or bronze flies, sometimes partly reddish. It is differentiated from Microdon s.s. in the key by the bare propleuron and the strongly produced lateral oral margins, of which the anterolateral corners are distinctly angular (Fig. 229). The latter character is presented with some hesitation, as it is uncertain whether it works for all species. Possibly, certain species here placed in Microdon s.s. also belong in this group. Therefore, the virgo-group is here considered as a species group within Microdon s.s., instead of within Microdon s.l. As it is presently uncertain which species should be assigned to it, this group is not recognized in the species catalogue in this paper.
Unplaced species. Several species of Microdon s.l. (see Appendix 2) do not fit into any of the groups described above. In the phylogenetic analyses of Reemer and Ståhls (in press), the following species belonging to this group were included: Microdon amabilis Ferguson, 1926, Microdon carbonarius Brunetti, 1923, Microdon nigromarginalis Curran & Bryan, 1926, Microdon pictipennis (Macquart, 1850), Microdon rieki Paramonov, 1957, Microdon trimacula Curran, 1928, Microdon tsara Keiser, 1971, Microdon waterhousei Ferguson, 1926 Kertész, 1910: 351. Misspelling. Myxogaster Shiraki, 1930 Description. Body length: 9-15 mm. Slender flies with constricted abdomen, wasplike. Head wider than thorax. Face convex or almost straight in profile; about as wide as an eye or narrower. Lateral oral margins not produced. Vertex flat. Occiput narrow, except slightly widened dorsally. Eye bare. Eyes in male not or hardly converging at level of frons, with mutual distance 4 to 5 times as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna longer or shorter than distance between antennal fossa and anterior oral margin; basoflagellomere shorter to longer than scape, oval; bare. Postpronotum pilose. Scutellum semicircular; without calcars. Anepisternum with weak sulcus; entirely bare or pilose anterodorsally, or pilose anterodorsally and along posterodorsal margin. Anepimeron entirely pilose or bare on ventral half. Katepimeron convex; bare. Wing vein R4+5 without posterior appendix. Vein M with small anterior appendix into cell r4+5. Vein M1 either straight or with anterior part directed outward, with one or two angles, whether or not with small inward appendix and /or small outward appendix. Postero-apical corner of cell r4+5 angular. Crossvein r-m located betwee basal 1/4 to 2/5 of cell dm. Abdomen constricted at base, with tergite 2 varying in length and width. Tergites 3 and 4 not fused. Male genitalia: phallus unfurcate, bent dorsad, with either lateral or dorsal combined with ventral lamellae, sometimes with apical spines; hypandrium with bulb-like base and apical part consist-ing of separate lobes, or hypandrium entirely consisting of two separate parts, which are not interconnected; epandrium without ventrolateral ridge; surstylus of varying shape.
Discussion. An important diagnostic character of Mixogaster, the anterior appendix of vein M, is also found in Spheginobaccha de Meijere, 1908 and certain specimens of Aristosyrphus primus. These taxa also share the character of the apical part of the hypandrium consisting of two separate lobes. See genus account of Aristosyrphus for discussion.
The morphology of the male genitalia is remarkably diverse in this genus, much more so than in other groups of Microdontinae (except perhaps Aristosyrphus / Eurypterosyrphus). Some species have characters not known from any other Microdontinae. Some examples are illustrated in Figs 245-248. In Mixogaster breviventris Kahl, 1897, the phallus has wide dorsal and ventral lamellae (Fig. 245). This type of genitalia is found in all Nearctic species, which also have a straight vein M1 in common. In M. thecla Hull, 1954 (Fig. 247), the hypandrium consists of two separate lobes, which are not interconnected ventrally to envelope the phallus, as is the case in all other studied Microdontinae. Besides, the subepandrial sclerite is strongly developed in this species, and produced well beyond the epandrium in lateral view. In an undescribed species (Fig. 248), the phallus is asymmetric in ventral view, with wide lateral lamellae, which are apically densely occupied with irregular spines. This is the only known case of asymmetric genitalia among Microdontinae. The spinose phallus is also a unique character.
The keys to the species by Hull (1954) and Carrera and Lenko (1958) (Brazilian species only) work reasonably well, but the existence of several undescribed species makes it necessary to check original descriptions or, preferably, type material in order to verify identifications. Considering the large interspecific variation in the male genitalia, these characters should be further explored in future (re)descriptions of species.
Diversity and distribution. Discussion. Hull (1937a) described Oligeriops as a genus, with only Microdon chalybeus Ferguson, 1926 included, without indicating its diagnostic generic characters. Hull (1949) used the reduced size of the eyes (due to widened occiput and gena) and the sickle-shaped antenna as key characters. Thompson and Vockeroth (1989) list Oligeriops as synonym of Microdon. Cheng and Thompson (2008) express their doubts about ranking Oligeriops as a genus, while referring to the antennae of Australian Microdon species as illustrated in Ferguson (1926b). These illustrations show that other species originally described in Microdon also have a curved basoflagellomere, just like M. chalybeus Ferguson, 1926, but nevertheless these species were not included in Oligeriops by Hull (1937aHull ( , 1949. Cheng and Thompson (2008) state that 'Whether these other species have reduced eyes remains to be seen!'. However, as Ferguson (1926a, b) already noticed, the four species he described are all 'close' and 'very similar'. Examination of type specimens, additional material and original descriptions, has confirmed this, and has made clear that all five species presently included in Oligeriops have reduced eyes and sickle-shaped basoflagellomeres indeed. Based on these and other morphological similarities, there is no doubt that they are closely related.
Oligeriops does not fit into the concept of Microdon s.s. as defined in the present paper. In addition to the reduced size of the eye and the curved basoflagellomere, the following characters distinguish Oligeriops from Microdon: anepisternum almost entirely pilose, at most with small bare part ventrally; propleuron bare; postero-apical corner of cell r4+5 rectangular; phallus projecting little beyond apex of hypandrium, furcate near apex. Considering these characters in combination with the results of Reemer and Ståhls (in press), it is deemed not appropriate to include this taxon in Microdon.
Diversity and distribution. Description. Body length: 7-9 mm. Small, dark flies with relatively short antennae and characteristically shaped abdomen. Head slightly wider than thorax. Face convex; about as wide as or narrower than an eye. Lateral oral margins hardly produced. Vertex flat or slightly produced, densely pilose. Occiput ventrally narrow, dorsally widened. Eye bare. Eye margins in male slightly converging at level of frons, with mutual distance 2.5-3 times width of antennal fossa. Antennal fossa about as wide as high. Antenna shorter than distance between antennal fossa and anterior oral margin; basoflagellomere as long as or longer than scape, oval; bare. Postpronotum pilose. Scutellum semicircular; with calcars. Anepisternum sulcate; entirely pilose. Anepimeron entirely pilose. Katepimeron moderately convex; with wrinkled texture; bare. Wing: vein R4+5 with posterior appendix; vein M1 perpendicular to vein R4+5; postero-apical corner of cell r4+5 rectangular to weakly rounded, with small appendix; crossvein r-m located between basal 1/6 to 1/5 of cell dm. Abdomen 2.5-3 times as long as wide; with characteristic shape: widest point about halfway tergite 2, which has strongly arcuate lateral margins and pair of depressed areas dorsally; tergites 3-4 narrower and almost parallelsided. Tergites 3 and 4 fused. Sternite 1 pilose. Male genitalia: phallus furcate near apex, with dorsal process long and whip-like, ventral process very short; epandrium with ventrolateral ridge. Diagnosis. Vein R4+5 with posterior appendix. Antenna shorter than distance between antennal fossa and anterior oral margin. Tergite 2 with strongly arcuate lateral margins, tergites 3-4 narrower and almost parallel-sided. Sternite 2 and 3 separated by membrane that is much less wide than sternite 2.
Discussion. This group was treated as a subgenus of Microdon by Thompson (1981b). Based on the phylogenetic evidence of Reemer and Ståhls (in press) this ranking cannot be maintained. Instead, Omegasyrphus is treated as a distinct genus. Thompson (1981b), who gives a key to the North American species, points out that species level taxonomy is necessary for this genus. This is still true.
Diversity and distribution. Described species: 5. North and Central America, from South Dakota in the U.S.A. southward to Guatemala. The south border of this range is marked by Microdon brunnipennis Hull, 1944, which was described as a variety of M. baliopterus Loew, 1872 by Hull (1944b). The assignment of this taxon to Omegasyrphus is based only on this description, as the type has not been examined.
Description. Body length: 4-5 mm. Small flies with short antennae and oval abdomen. Head slightly wider than thorax. Face convex; narrower than an eye. Lateral oral margins not produced. Vertex flat. Occiput ventrally narrow, dorsally widened. Eye bare. Eye margins in male not converging at level of frons, with mutual distance about three times as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna shorter than distance between antennal fossa and anterior oral margin; basoflagellomere longer than scape, oval, about 1.5 times as long as wide, bare. Postpronotum pilose. Scutellum semicircular; without calcars. Anepisternum convex; pilose anteriorly and posterodorsally, widely bare in between. Anepimeron bare or with a few thick, seta-like pile dorsally. Katepimeron convex; bare. Wing: vein R4+5 without posterior appendix; vein M1 straight, perpendicular to vein R4+5; postero-apical corner of cell r4+5 rectangular, with small appendix; crossvein r-m located very close to base of cell dm. Abdomen oval, about 1.5 times as long as wide. Tergites 3 and 4 fused. Sternite 1 bare. Male genitalia: phallus unfurcate, straight, projecting only little beyond apex of hypandrium; hypandrium with bulb-like base; epandrium without ventrolateral ridge; surstylus unfurcate. Diagnosis. Abdomen oval; yellow and black. Vein R4+5 without posterior appendix. Crossvein r-m almost at same level as base of cell dm. Antenna shorter than distance between antennal fossa and anterior oral margin. Postpronotum pilose.
Discussion. When Thompson (1969) described this genus, he stated that it appeared to be the most primitive microdontine fly known. This was based on a number of presumed plesiomorphic characters: 1) unsclerotized ejaculatory apodeme and sac; 2) short antenna; 3) underdeveloped and bare metasternum; 4) lack of basal setal patches on hind femur; 5) lack of a spurious vein; 6) lack of appendix on vein R4+5; 7) presence of a double sustentacular apodeme; 8) unfurcate phallus. Now that a larger number of taxa of Microdontinae could be studied, all of these characters were also found in other taxa (Reemer and Ståhls in press), except for the unsclerotized ejaculatory apodeme. See also discussion under Surimyia.
Description. Body length: 4-11 mm. Small, slender flies with short antennae and more or less parallel-sided abdomen. Head slightly wider than thorax. Face convex; narrower than an eye. Lateral oral margins not produced. Vertex flat. Occiput ventrally narrow, dorsally strongly widened. Eye bare. Eye margins in male only slightly converging at level of frons, with mutual distance 1.5-2.5 times as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna shorter than distance between antennal fossa and anterior oral margin; basoflagellomere longer than scape, oval, about 1.5 times as long as wide, bare. Postpronotum pilose. Scutellum semicircular; without calcars. Anepisternum convex; pilose anteriorly and posteriorly, widely bare in between. Anepimeron entirely pilose. Katepimeron convex; bare. Wing: vein R4+5 without posterior appendix; vein M1 straight, perpendicular to vein R4+5; postero-apical corner of cell r4+5 rectangular, with small appendix; crossvein r-m located within basal 1/10 of cell dm. Abdomen elongate: more or less parallel-sided, may be subtly constricted at tergite 3 (male), or slightly oval (female); 2.5-4 times as long as wide. Tergites 3 and 4 fused (but distinct suture visible). Sternite 1 bare or pilose. Sternites 3-4 strongly narrowed; narrower than sternite 2, with wide membraneous parts laterally. Male genitalia: phallus furcate near apex, slightly bent dorsad, projecting well beyond apex of hypandrium; hypandrium with apical part consisting of two separate lobes; epandrium without ventrolateral ridge; surstylus of varying shape. Diagnosis. Vein R4+5 without posterior appendix. Postpronotum pilose. Antenna shorter than distance between antennal fossa and anterior oral margin. Vein M1 straight, not parallel to wing margin, perpendicular to both vein R4+5 and M. Mesonotum with transverse suture incomplete. Sternites 3-4 strongly narrowed; narrower than sternite 2, with wide membraneous parts laterally.
Discussion. The synonymy of Syrphinella Hervé-Bazin, 1926 with Paramicrodon was suspected by Hull (1937a) and stated explicitly by Hull (1949). This subjective synonymy is here confirmed, based on examination of the type specimen of the type species. Myxogasteroides Shiraki, 1930 was treated as a synonym of Paramicrodon by Hull (1949) and Cheng and Thompson (2008), a synonymy followed here based on the description of the type species. The synonymy of Nannomyrmecomyia  and Paramicrodon was stated by Thompson (1969Thompson ( , 1981a and is also confirmed here based on examination of the type specimens. Diversity and distribution. Described species: 8. The range of this genus is interestingly disjunct, with six species from the Oriental Region (Thailand to Moluccas), one from New Guinea and two from the Neotropical region. At least one additional species occurs in the Neotropical region (unpublished observations by the first author), but more species-level work is needed to sort this out. Description. Body length: 5-13 mm. Slender flies with constricted abdomen and long antennae, usually with black and yellow colour pattern, wasp mimics. Head wider than thorax. Face convex in profile; narrower than to wider than an eye. Lateral oral margins not produced. Vertex flat to strongly swollen. Occiput ventrally narrow, dorsally widened. Antennal fossa about as wide as high. Eye bare. Eye margins in male parallel, not converging at level of frons. Antenna longer than distance between antennal fossa and anterior oral margin. Basoflagellomere usually much longer than scape, except shorter in P. illucens (Bezzi)  Basoflagellomere at least three times as long as wide. Posterio-apical corner of wing cell r4+5 rectangular or somewhat acute. Abdomen usually constricted (i.e. with narrowest point at tergite 2 and widest point at tergite 3 or 4); if not, then the following three characters apply: 1) basoflagellomere 2-4 times as long as scape, 2) tergite 2 less than half as long as tergites 3 and 4 together, 3) face smooth medially (without vitta of transversely wrinkled texture).
Discussion. Cheng and Thompson (2008) regarded Paramixogasteroides Shiraki, 1930 andTanaopicera Hull, 1945 as subjective synonyms of Paramixogaster. Examination of the type species of Tanaopicera, Ceratophya variegata Walker, 1852, confirmed this opinion with regard to Tanaopicera. One of the characters  used to characterize Tanaopicera was 'the high, greatly developed vertex'. However, the vertex in the holotype of C. variegata is neither high nor greatly developed. This species is very similar to other Paramixogaster-species in all important characters. The type species of Paramixogasteroides, Myxogaster variegata Sack, was not examined, but its description by Sack (1922) is clear enough to include this taxon in Paramixogaster.
Morphological variation among the species presently included in Paramixogaster is large. Although most species have a constricted abdomen in dorsal view, this is not the case in the African taxa P. acantholepidis (Speiser, 1913) and P. crematogastri (Speiser, 1913), and the Australian species P. praetermissus (Ferguson, 1926). However, tergite 2 is dorsoventrally flattened in these species, so in lateral view their abdomen appears constricted. In all other important characters of external morphology and male genitalia these taxa belong in Paramixogaster, as corroborated by the results of the phylogenetic analysis based on morphology (Reemer and Ståhls in press).
Paramixogaster illucens (Bezzi, 1915) and P. luxor (Curran, 1931) are the only species included in this genus in which the basoflagellomere is shorter than the scape. In P. luxor, the shape of the surstylus also differs from the other species, as it consists of three separate branches (Fig. 282). Nevertheless, both species are included in Paramixogaster because agree with the diagnosis.
Paramixogaster contractus , P. conveniens  and P. omeanus (Paramonov, 1957) are aberrant from all other known species of Paramixogaster in their complete transverse suture. This character is also found in Indascia, which includes species which look superficially similar to these Paramixogaster-species. However, these species are here assigned to Paramixogaster, based on the phylogenetic analysis of their morphology (Reemer and Ståhls in press). In addition, they possess a diagnostic character for Paramixogaster: the bare postpronotum. The first two species, P. contractus and P. conveniens, differ from all other studied species of Microdontinae in the presence of pile on the metaepisternum. It will be interesting to re-evaluate their taxonomic affinities when additional material becomes available. At present, the species are only known from the holotypes, which both are females, so no characters of male genitalia or DNA could be analyzed.
As a consequence of transferring some species from other genera to Paramixogaster, replacement names had to be chosen for two species. Examination of the type of Microdon vespiformis de Meijere, 1908 made clear that this is a species of Paramixogaster. As Mixogaster vespiformis Brunetti, 1913 was later designated as the type species of Paramixogaster, these two names are now secondary homonyms. For the junior name, vespiformis Brunetti, the nomen novum Paramixogaster brunettii is proposed here. The other new name introduced here is Paramixogaster sacki for Paramixogasteroides variegata Sack, 1922, which is a junior secondary homonym of Ceratophya variegata Walker, 1852.
Diversity and distribution. Described species: 26. Afrotropical (5 species), Oriental (12) and Australian region (9). Several additional species, from all three regions, await description. ; postero-apical corner of cell r4+5 widely rounded; crossvein r-m located around basal 1/6 of cell dm. Abdomen elongate, more than 3 times as long as wide; in male gradually tapering from anterior half of tergite 2 to apex; in female slightly constricted between tergites 3 and 4. Tergites 3 and 4 fused. Male genitalia: phallus furcate basally, with dorsal process much longer than ventral one, projecting far beyond apex of hypandrium; epandrium with ventrolateral ridge; surstylus weakly furcate, divided into two short lobes. Diagnosis. Vein R4+5 with posterior appendix. Postpronotum pilose. Anepisternum almost entirely pilose, except bare on small ventral part. Basoflagellomere shorter than scape. Abdomen at least three times as long as wide. Tergite 2 with pair of depressed areas (Fig. 287).
Discussion. When Shiraki (1930) described Parocyptamus, this genus was diagnosed in a key by the following two characters: abdomen narrow and elongate, frons with antennal prominence ('Fühlervorsprung'). The latter character is of limited use, as the frons is more or less extended above the antennae in many other taxa of Microdontinae. Hull (1937a) did not state which characters he considered diagnostic in his description of Stenomicrodon. Judging from his remarks in Hull (1949), the shape of the abdomen and the presence of a patch of short, spinose setae at the base of the front and mid femora were considered important characters. Although the anterobasal patches of setae are well-developed, such patches are also found in several other taxa of Microdontinae. Perhaps the spines are somewhat stronger developed than in most taxa, but it is hard to describe this as a discrete character state. Therefore, this character is not used in the present key and Diagnosis.
The abdomen is constricted (slightly) only in the female, not in the male, as might be erroneously concluded from the key of Cheng and Thompson (2008).
The synonymy of Stenomicrodon with Parocyptamus was already established by Hull (1949). Examination of the involved type specimens by the first author has confirmed this (subjective) synonymy. The type species of both genus group names are here also considered as synonyms (Parocyptamus sonamii Shiraki, 1930= Stenomicrodon purpureus Hull, 1937 syn. n.). Microdon stenogaster Curran, 1931 also belongs to this genus, as it is almost identical to the type species in colouration, external morphology and male genitalia. Closer examination of available specimens, also from Sumatra and Thailand, is necessary to resolve species level taxonomy. Shiraki (1930) based his description of Parocyptamus sonamii on three males. Two of these syntypes are kept in the NIAS collection. The third male (from Sokotsu) is apparently lost. Label information is as follows. Syntype 1: label 1: "Formosa, Shinchiku, -18. VII 1-30. J. Sonan, K. Miyake"; label 2: "Parocyptamus sonamii"; label 3 (round, red-bordered): "Type". Syntype 2: label 1: "CIHpOn, 17.VII.1922, M. Yoshino"; label 2 (round, red-bordered): "Type". The date on the label of syntype 1 is a bit cryptic ("-18. VII 1-30"). It is unlikely to assume the specimen has been collected in July 1930, because Shiraki's work was published on the 30th of January 1930. It seems more plausible that the date was 1-30 July 1918. Shiraki (1930)  Description. Body length: 6-18 mm. Slender to moderately broadly built flies with oval or basally constricted abdomen and long antennae. Head wider than thorax. Face straight to slightly convex or slightly concave in dorsal half; narrower to wider than an eye; medially with vitta of transversely wrinkled texture (except in some smaller species of the flavofascium-group); gena distinctly ventrally produced. Lateral oral margins produced. Vertex flat. Occiput ventrally narrow, dorsally widened. Eye bare. Eye margins in male converging at level of frons, with mutual distance 1.5-4 times as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna longer than distance between antennal fossa and anterior oral margin; basoflagellomere shorter to longer than scape; bare. Postpronotum pilose or bare. Scutellum semicircular; with calcars. Anepisternum sulcate; pilose anterodorsally and posteriorly, widely bare in between. Anepimeron entirely pilose. Katepimeron flat; with wrinkled texture; bare. Wing: vein R4+5 with posterior appendix; vein M1 more or less straight, perpendicular to vein R4+5; postero-apical corner of cell r4+5 widely rounded, without appendix; crossvein r-m located between basal 1/6 and 1/3 of cell dm. Abdomen oval or basally constricted, 2-4 times as long as wide. Tergites 3 and 4 fused. Sternite 1 bare. Male genitalia: phallus not or little projecting beyond apex of hypandrium, slightly bent dorsad, shallowly furcate, with both processes about equally long and with their apexes wide at the furcation point but pointed apically; epandrium without ventrolateral ridge; surstylus unfurcate.
Diagnosis. Vein R4+5 with posterior appendix. Postero-apical corner of cell r4+5 widely rounded. Katepimeron flat, with wrinkled texture, bare. Face in profile slightly convex, straight or slightly concave, but never bulged in ventral half. Vertex flat.
Three species groups are recognized here. These groups may not be monophyletic, but they may be useful for purposes of species identification. They are diagnosed as follows: bidens-group: Abdomen oval or parallel-sided. Tergites without golden pile. Basoflagellomere less than twice as long as scape.
flavofascium-group: Abdomen oval. Tergite 4 often with golden or silver pile. If not, then basoflagellomere more than twice as long as scape.
trivittatus-group: Abdomen constricted basally. Discussion. The species here assigned to this genus (see Appendix 2) used to be placed in Microdon (e.g. Thompson et al. 1976), but the results of the phylogenetic analyses by Reemer and Ståhls (in press) indicate that they do not belong there. Based on external characters this group is difficult to diagnose, but usually the species can be distinguished at a glance from those of Microdon because of their more or less elongate (sometimes constricted) abdomen. In addition, morphology of the phallus is very constant (differences with Microdon in parentheses): projecting not or little beyond apex of hypandrium (far beyond apex of hypandrium), slightly bent dorsad (strongly bent), shallowly furcate (deeply furcate), with both processes about equally long and with their apexes wide at the furcation point but pointed apically.
Only one species here included in Peradon was previously not classified in Microdon: Ubristes chrysopygus Giglio-Tos, 1892.
Diversity and distribution. Described species: 24. Neotropical. Several undescribed species are known to the first author.
Etymology. The generic name is a combination of the Greek words peras (west) and odon, with the latter used as a suffix derived from Microdon. The prefix pera-is used to emphasize that this genus is restricted in its distribution to the western hemisphere. Type species: Piruwa phaecada spec. n. Type locality: Peru, Sachavacayoc.
Description. Body length: 4 mm. Small, slender flies with short antennae and constricted abdomen. Head slightly wider than thorax. Face convex; narrower than an eye. Lateral oral margins not produced. Vertex flat. Occiput narrow over entire length. Eye bare. Eye margins in male not converging at level of frons, with mutual distance 3 times as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna shorter than distance between antennal fossa and anterior oral margin; basoflagellomere longer than scape, oval, about twice as long as wide, bare. Postpronotum bare. Scutellum semicircular; without calcars; with long bristly pile along margin, clearly longer and thicker than pile on rest of scutellum. Anepisternum convex; pilose anterodorsally and along posterodorsal margin. Anepimeron pilose along dorsal margin. Katepimeron convex; bare. Wing: vein R4+5 without posterior appendix; vein M1 straight, perpendicular to vein R4+5; postero-apical corner of cell r4+5 rectangular, with small appendix; crossvein r-m located within basal 1/10 of cell dm. Abdomen constricted, narrowest at transition between tergites 1 and 2, widest at tergite 4; about 2.5 times as long as wide. Tergites 3 and 4 fused, no suture visible. Sternite 1 bare. Male genitalia: phallus furcate near apex, slightly bent dorsad, projecting only a little beyond apex of hypandrium; hypandrium with bulb-like base, with apical part entire, not consisting of two separate lobes; epandrium without ventrolateral ridge; surstylus consisting of two lobes, with basal lobe angular, apical lobe rounded.
Discussion. Although there is a superficial similarity in habitus to Paramicrodon (small, slender, short antennae, vein R4+5 without posterior appendix), Piruwa differs from that genus in the following important characters: occiput narrow over entire length; postpronotum bare; scutellum with long bristly pile along margin; anepimeron pilose only along dorsal margin; sternites 3-4 about as wide as sternite 2; hypandrium with apical part not consisting of two separate lobes. Considering these differences, a close relationship between these taxa seems unlikely. Because of these differences and the uncertainy of taxonomic affinities, this distinct taxon is given generic rank.
Diversity and distribution. Described species: 1. Neotropical. Only known from Peru.
Etymology. The name Piruwa is derived from Piruw, the word for Peru in Quechuan, a native Andean-Ecuadorian language. It is to be treated as feminine. Description. Body length: 7-9 mm. Slender flies with long antennae and petiolate abdomen. Head a little wider than thorax. Face more convex or straight in profile; narrower than to as wide as an eye. Lateral oral margins weakly produced. Vertex convex and shining; sparsely pilose, sometimes bare on anterior half. Occiput ventrally narrow, dorsally strongly widened. Eye bare or with very short and sparse pile. Eye margins in male converging at level of frons, with mutual distance 1-2 times width of antennal fossa. Antennal fossa about as wide as high to 1.5 times as wide as high. Antenna longer than distance between antennal fossa and anterior oral margin; basoflagellomere shorter to longer than scape, oval; bare. Postpronotum pilose. Scutellum semicircular; with or without calcars. Anepisternum sulcate; entirely pilose or widely bare medially. Anepimeron entirely pilose. Katepimeron flat to convex; usually with wrinkled texture; bare. Wing: vein R4+5 with posterior appendix; vein M1 perpendicular to vein R4+5; postero-apical corner of cell r4+5 widely rounded to rectangular, with or without small appendix; crossvein r-m located between basal 1/6 to 1/3 of cell dm. Abdomen elongate, more than three times as long as wide, constricted, with narrowest point between halfway tergite 2 and transition between tergites 2 and 3. Tergites 3 and 4 fused. Sternite 1 pilose or bare. Male genitalia: phallus furcate near apex, with dorsal process long and whip-like, ventral process very short; epandrium with ventrolateral ridge. Diagnosis. Vein R4+5 with posterior appendix. Vertex convex and shining, sparsely pilose to bare. Abdomen petiolate, except parallel-sided in P. biluminiferus Hull, but tergite 2 distinctly dorsoventrally flattened in that species.

Pseudomicrodon
Discussion. Among Microdontinae with a petiolate abdomen, Pseudomicrodon species are recognized by their convex and shining vertex. Microdon biluminiferus Hull, 1944 is the only included species without a petiolate abdomen. Instead, the abdomen is parallel-sided, but in lateral view appears constricted because of the dorsoventrally flattened segment 2. This species is assigned to Pseudomicrodon based on the convex vertex and the morphology of the male genitalia (Fig. 319, 320), combined with the results of the phylogenetic analysis of morphological characters (Reemer and Ståhls in press).
At present, the basis for distinguishing Ceriomicrodon, Pseudomicrodon and Rhopalosyrphus is narrow. The groups are certainly related, but as presently defined it is doubtful whether they are monophyletic, considering the variation in several morphological characters. Keiser (1971) described Pseudomicrodon elisabethae from Madagascar. This species is here included in Paramixogaster. Cheng and Thompson (2008) mention the similarity of the South African taxon Microdon illucens Bezzi, 1915 to Pseudomicrodon, which is here also included in Paramixogaster.
Diversity and distribution. Discussion. Bezzi (1915) distinguished Ptilobactrum from Microdon species by the "breadth of the head, the face being furrowed, and by the unusual shape of the antennae." Indeed, the grooves on the face, running fom the lunula obliquely downward to the eye margins, are quite unusual among Microdontinae. They are reminescent of the ptilinal sutures of Diptera Schizophora. Similar grooves are found in certain species of Furcantenna, Schizoceratomyia, Paramixogaster and Thompsodon, but usually less distinct. The antennae are unusual in their long pilosity, a character shared with Ceratrichomyia, Furcantenna, Kryptopyga and Schizoceratomyia.
See Ceratrichomyia for a discussion on synonymy of that genus with Ptilobactrum, as proposed by Cheng and Thompson (2008).
Description. Body length: 5-10 mm. Stingless bee mimicking flies with short to moderately long antennae and oval, kite-shaped or more or less parallel-sided abdomen. Head slightly wider than thorax. Face convex; narrower than an eye. Lateral oral margins not produced. Vertex narrow, convexly produced and shining in most species, flat in some. Occiput wide and parallel-sided over entire length. Eye with short, sparse pile. Eye margins in male not converging at level of frons, with mutual distance 2 to 3 times as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna as long as or shorter than distance between antennal fossa and anterior oral margin; basoflagellomere shorter to longer than scape, oval; bare. Postpronotum pilose. Scutellum semicircular, in some species weakly sulcate apicomedially; without calcars. Anepisternum without sulcus; pilose anterodorsally and posteriorly, widely bare in between. Anepimeron entirely pilose. Katepimeron convex; bare. Metapleurae either separated or forming postmetacoxal bridge. Wing: vein R4+5 without posterior appendix; vein M1 perpendicular to vein R4+5; postero-apical corner of cell r4+5 rectangular, with small appendix; crossvein r-m located within 1/4 of cell dm, usually within basal 1/10. Abdomen oval or kite-shaped, 1.5 to 2.5 times as long as wide. Tergites 3 and 4 fused. Sternite 1 pilose or bare. Male genitalia: phallus furcate near apex, with dorsal and ventral process equally long; epandrium without ventrolateral ridge. Diagnosis. Vein R4+5 without posterior appendix. Occiput widened and parallelsided over entire length.
Discussion. In some species (e.g. R. mellea (Curran, 1940), R. maculata (Shannon, 1927)) the metapleura are separated and do not form a postmetacoxal bridge. So far in Microdontinae, this character state was known only in the genus Spheginobaccha (Cheng and Thompson 2008).
The type specimen of the type species, Rhoga lutescens Walker, 1857, is not present in the BMNH-collection (pers. comm. N. Wyatt), where it is supposed to be according to Thompson et al. (1976) and Thompson (2010). Apparently it is lost.
Description. Body length: 9-15 mm. Slender flies with long antennae and petiolate abdomen. Head a little wider than thorax. Face more or less convexly produced on ventral half; narrower than an eye. Lateral oral margins produced. Vertex flat, entirely pilose. Occiput ventrally narrow, dorsally strongly widened. Eye bare. Eye margins in male converging at level of frons, with mutual distance 1-2 times width of antennal fossa. Antennal fossa about 1.5 times as wide as high. Antenna longer than distance between antennal fossa and anterior oral margin; basoflagellomere longer than scape, oval; bare. Postpronotum pilose. Scutellum semicircular; with or without calcars, if present, then small and with mutual distance small. Anepisternum convex or with weak sulcus; entirely pilose. Anepimeron entirely pilose. Katepimeron flat to weakly convex; with wrinkled texture; bare, partly pilose or entirely pilose. Wing: vein R4+5 with posterior appendix; vein M1 perpendicular to vein R4+5; postero-apical corner of cell r4+5 widely rounded to rectangular, with or without small appendix; crossvein r-m located between basal 1/8 to 1/4 of cell dm. Abdomen elongate, more than three times as long as wide, constricted, with narrowest point between halfway tergite 2 and transition between tergites 2 and 3. Tergites 3 and 4 fused. Sternite 1 pilose or bare. Male genitalia: phallus furcate near apex, with dorsal process long and whip-like, ventral process very short; epandrium with ventrolateral ridge. Diagnosis. Vein R4+5 with posterior appendix. Abdomen petiolate. Vertex flat, entirely pilose. Postpronotum pilose. Mesonotal transverse suture incomplete. Tergites 3 and 4 fused. Anterior margin of tergite 2 at least twice as wide as posterior margin. Rhopalosyrphus s.s.: katepimeron pilose. Rhopalosyrphus s.l.: katepimeron bare.
Discussion. Previous authors have defined this genus more strictly than is done in the present paper. Weems et al. (2003) and Cheng and Thompson (2008) only included species with a pilose katepimeron. A number of additional species are known from the Neotropical region which are similar to Rhopalosyrphus auct. in most characters, but which have a bare or almost bare katepimeron. In R. robustus sp. n. the katepimeron is only narrowly pilose along the anterior margin. In all other characters, this species has the diagnostic characters of Rhopalosyrphus as described by Weems et al. (2003): abdomen petiolate, antenna longer than face, scape and basoflagellomere elongate, face produced ventrally (variable), occiput strongly widened dorsally, metasternum developed, hind tibia flared apically. The male genitalia of R. robustus are very similar to those of Rhopalosyrphus auct., with an apically furcate phallus, of which the dorsal process is very long and whip-like (Figs 352-355).
Microdon abnormis Curran, 1925 is also similar to Rhopalosyrphus in the characters mentioned above, but has a bare katepimeron. In the analysis of morphological characters by Reemer and Ståhls (in press), a closely related species (Rhopalosyrphus abnormoides sp. n.) is placed within Rhopalosyrphus.
Based on the results of the phylogenetic analyses and the (subjective) evaluation of external and genitalic characters, Rhopalosyrphus is here extended to include also the species with a bare or almost bare katepimeron, which includes species previously grouped in the abnormis group (see account of Pseudomicrodon in Cheng and Thompson 2008), as well as Microdon cerioides Hull, 1943. Species with a pilose katepimeron are included in Rhopalosyrphus s.s., while the other species are treated as Rhopalosyrphus s.l.
The inclusion of Rhopalosyrphus oreokawensis sp. n. in this genus is to be regarded as preliminary. Unlike the other species included in Rhopalosyrphus, this species has very short antennae, an oblique vein M1 and a more slender tergite 2. Analysis of its morphological characters (Reemer and Ståhls in press) resolves its phylogenetic position near Rhopalosyrphus. Possibly, it would be better to erect a new genus for this spe-cies. This is nevertheless not done here, in awaitance of a better understanding of the relationships of the taxa included in the 'Rhopalosyrphus-clade'.
Diversity and distribution. Description. Body length: 4-9 mm. Broadly built flies with long antennae (bifrucate in male) and oval abdomen. Head wider than thorax. Face slightly convex or medially concave; wider than an eye. Mouth parts weakly developed, small; oral opening small and round, with lateral margins not produced. Vertex more or less flat, not strongly produced or convex. Frontal ocellus normal, split in two medially or absent. Occiput ventrally narrow, dorsally weakly widened. Eye bare. Eyes in male not or only slightly converging at level of frons, with mutual distance 3-4 times the width of antennal fossa. Antennal fossa about as wide as high. Antenna longer than distance between antennal fossa and anterior oral margin. Basoflagellomere longer than scape, bifurcate in male, in some species also in female; both branches long pilose, especially on inner side; in one (undescribed) species occupied with more than 20 long, narrow tubercles. Arista in male well-developed (longer than pedicel) or reduced to a small stump (shorter than pedicel); in female well-developed, sometimes almost as long as basoflagellomere and thickened. Postpronotum pilose or bare. Scutellum semicircular; without calcars. Anepisternum convex, sometimes with weak sulcus in dorsal 1/4; pilose on dorsal 2/3 to 3/4. Anepimeron pilose on dorsal 3/4 to 1/4, or only along posterior margin. Katepimeron convex; bare; smooth. Wing: vein R4+5 without posterior appendix; vein M1 straight and perpendicular to vein R4+5, or with weak outward angle in anterior 1/2; postero-apical corner of cell r4+5 rectangular to widely rounded, with or without small appendix; crossvein r-m located between basal 1/8 and 1/4 of cell dm. Abdomen dorsoventrally flattened; more oval, with largest width at tergite 3; 1.5-2 times as long as wide. Tergites 3 and 4 fused. Male genitalia: phallus furcate near apex, straight or apically bent ventrad, projecting not or hardly beyond apex of hypandrium; hypandrium with bulb-like base; epandrium without ventrolateral ridge; surstylus unfurcate, elongate or wide. Diagnosis. Vein R4+5 without posterior appendix. Abdomen oval. Antenna longer than distance between antennal fossa and anterior oral margin. Antenna inserted below dorsal eye margin. Vertex more or less flat. Katepisternum bare. Metasternum bare.
Discussion. Hull (1949) and Papavero (1962) treated Schizoceratomyia as a synonym of Masarygus. See Masarygus for discussion on this synonymy, which is not followed here. These authors, as well as Cheng and Thompson (2008) also considered Johnsoniodon as a synonym of Schizoceratomyia, as is also done in the present paper. Although in the two species originally included in Schizoceratomyia (S. barretoi Carrera, Lopes & Lane, 1947 and S. flavipes Carrera, Lopes & Lane, 1947) the basoflagellomere is bifurcate in the male only, whereas in Johnsoniodon this character is found in the female, these taxa are otherwise very similar.
Apparently, Curran (1947) was unaware of the description of Schizoceratomyia by Carrera et al. (1947a, b) when his description of Johnsoniodon malleri Curran, 1947 was published, as this happened almost simultaneously. According to Van Doesburg (1966), the name Schizoceratomyia was published on the 3rd of July 1947, and Johnsoniodon on 14th of July 1947. Cheng and Thompson (2008) stated that Schizoceratomyia was published on the 12th of July 1947. Regardless of whether the date is 3 rd or 12 th of July Schizoceratomyia has priority over Johnsoniodon.
Besides S. malleri (Curran), a furcate basoflagellomere in the female is also found in Masarygus carrerai Papavero, 1962. This species is also included in Schizoceratomyia.
Remarkably, in some specimens of Schizoceratomyia, the frontal ocellus is split in two, strongly reduced or even absent, whereas the posterior ocelli are well-developed. Following present species definitions, different states for this character seem to occur within the same species. However, more taxonomic work at species-level is necessary to establish whether this character state variation is intra-or inter-specific. In most Diptera and other flying insects, all three ocelli are well-developed. Reduced or absent ocelli occur in certain terrestrial insects, like certain ants and cockroaches. Among Diptera, they are partly or entirely absent only in a few groups, apparently mainly in certain nematocerous families and some brachypterous or apterous taxa (Cumming and Wood 2009). It will be interesting to try to correlate the degree of development of the frontal ocellus to behaviour and lifehistory of Schizoceratomyia-species; aspects which are currently unknown, unfortunately.
Diversity and distribution. Described species: 4. Neoptropical. A few undescribed species are known to the first author. Discussion. Curran (1925a) erected Serichlamys as a subgenus of Microdon, but subsequent authors considered Serichlamys as a synonym of the typic subgenus of Microdon (Wirth et al. 1965, Thompson 1981b, Cheng and Thompson 2008. Curran (1925a) did not clearly state which characters he considered diagnostic. In his key, Curran keyed out the type species Microdon rufipes (Macquart, 1842) by its eyes being pilose, which was based on a translation of the original description of Aphritis rufipes. Indeed, Macquart (1842) wrote that this species has 'yeux peu velus' (eyes little pilose). However, examination of the type specimen (coll. OUMNH) revealed that its eyes are bare. Either pile have been wiped off or eroded in the course of time, or Macquart (1842) made an error in his description. Whether Aphritis rufipes has pilose eyes or not, Serichlamys is here recognized as distinct as all included species differ in other characters from Microdon s.s., e.g. postero-apical corner of cell r4+5 rectangular (rounded in Microdon s.s.), phallus furcate apically, hypandrium with bulb-like base.

Serichlamys
The differences with Microdon s.s. could be used as arguments for reinstating the subgeneric status of Serichlamys. However, a subgeneric status is contradicted by the phylogenetic results of Reemer and Ståhls (in press), who recovered two Neotropical species of Serichlamys as sister group to Archimicrodon, without apparent close affinities to Microdon. The type species S. rufipes and S. scutifer (Knab, 1917) were included in a phylogenetic analysis based only on morphology, and placed in a large and rather uninformative polytomy, but not within a clade containing species of Microdon s.s. For this reason, Serichlamys is here raised to genus level.
Three Nearctic species are included in Serichlamys: S. rufipes (Macquart, 1842), S. scutifer (Knab, 1917), and S. diversipilosus (Curran, 1925). The latter species is included with uncertainty, based only on the description, as no specimens were examined. Two Neotropical species are included: S. mitis (Curran, 1940) and S. mus (Curran, 1936). The Neotropical species differ from the Nearctic ones in the shape of the surstylus, which has a long posterior process which is lacking in the Nearctic species. Otherwise the species are very similar. Species of Serichlamys quite similar to the Old World genus Archimicrodon in general habitus and important morphological characters, including the male genitalia. Generally, the antennae of Serichlamys-species are longer and the scutellar calcars are longer.
Diversity and distribution. Described species: 4 or 5. Nearctic (2 or 3 described species) and Neotropical (2 described species). Several undescribed species from the Neotropical regioan are known to the first author. Description. Body length: 7-19 mm. Slender flies with short antennae and constricted abdomen. Head about as wide as to wider than thorax. Face in profile straight to slightly concave in dorsal 2/3, with a faint convex tubercle in ventral 1/3; narrower than an eye. Lateral oral margins not produced. Vertex flat. Occiput narrow ventrally, widening dorsally, with distinct crease in dorsal 2/3. Eye bare (African species) or short pilose (Oriental species). Eyes in male not (African species) or strongly (Oriental species) converging at level of frons, in one Oriental species (S. chilcotti Thompson) even nearly contiguous. Antennal fossa about twice as wide as high. Antenna shorter than distance between antennal fossa and anterior oral margin. Basoflagellomere longer than scape, oval, except more or less triangularly enlarged in males of some African species; bare. Postpronotum pilose. Scutellum semicircular; without calcars. Anepisternum without sulcus; entirely sparsely pilose, sparsely pilose only posteriorly, or entirely bare. Anepimeron pilose on dorsal half or bare. Katepimeron flat; bare or pilose; smooth. Wing vein R4+5 without posterior appendix. Vein M1 oblique and more or less parallel to wing margin, in African species only so in anterior 1/2, posterior 1/2 straight. Postero-apical corner of cell widely rounded and without appendix in Oriental species, rectangular and with appendix in African species. Crossvein r-m located between basal 1/6 to 1/3 of cell dm. Abdomen constricted, narrowest halfway or at posterior margin of tergite 2, widest at tergite 4. Tergites 3 and 4 fused. Male genitalia: phallus unfurcate, straight (African species) or bent dorsad (Oriental species), articulating with hypandrium apically (perialla-group) or basally (macropoda-and rotundiceps-group); hypandrium with apical part consisting of separate lobes; epandrium without ventrolateral ridge; surstylus unfurcate, oval or more or less rectangular to triangular. Diagnosis. Metapleura not connected, not forming a postmetacoxal bridge. Abdomen constricted. Occiput with deep crease on dorsal 2/3. Discussion. Hull (1949) was the first to include Spheginobaccha in the Microdontinae. Thompson (1969) excluded it, after which Ståhls et al. (2003) included it again. The latter placement was based on a sister-group relationship of Spheginobaccha to all other Microdontinae, as recovered in a phylogenetic analysis of combined molecular and morphological characters. Species can be identified using Thompson (1974), supplemented with Dirickx (1995).
Dexiosyrphus was described by Hull (1949) as a subgenus of Spheginobaccha, based on S. rotundiceps (Loew, 1857). Thompson (1974) argued that if Dexiosyrphus was to be recognized, then another subgenus would have to be erected for the perialla-group. He considered this unnecessary, as the three species groups he recognized were sufficient for proper segregation of the species. We see no reason to adopt a different point of view.
Diversity and distribution. Description. Body length: 6-11 mm. Stingless bee mimicking flies with moderately long antennae and more or less triangular abdomen. Head slightly wider than thorax. Face in profile straight to convex; narrower to wider than an eye. Lateral oral margins hardly to moderately produced. Vertex flat, convex or irregularly swollen. Occiput narrow ventrally, slightly widened dorsally. Eye bare. Eye margins in male converging at level of frons, with mutual distance 1-3 times width of antennal fossa. Antennal fossa about as wide as high. Antenna shorter to longer than distance between antennal fossa and anterior oral margin; basoflagellomere shorter to longer than scape, oval; bare. Postpronotum pilose. Scutellum semicircular, sometimes weakly sulcate apicomedially; without calcars. Anepisternum convex, without sulcus; anterodorsally pilose, posteriorly pilose or bare, widely bare in between. Anepimeron with pile limited to dorsal half, if pilose on ventral half then only sparsely. Katepimeron convex; bare. Wing: vein R4+5 usually with posterior appendix (seldomly missing); vein M1 perpendicular to vein R4+5; postero-apical corner of cell r4+5 widely rounded to rectangular, with or without small appendix; crossvein r-m located between basal 1/5 to 1/3 of cell dm. Abdomen widest at tergite 2, with next tergites either gradually narrowing (kite-shaped abdomen) or more or less parallel-sided; 1.5 to 3.5 times as long as wide. Antetergite almost fused to tergite 1; in most species enlarged, concave and smooth. Tergites 3 and 4 fused. Sternite 1 bare. Male genitalia: phallus unfurcate, bent dorsad, in most species projecting beyond apex of hypandrium; hypandrium with bulb-like base; epandrium without ventrolateral ridge; surstylus in most species with two wide lobes, but other shapes also occur. Diagnosis. Sternites 2 and 3 separated by membraneous part as wide as or wider than sternite 2.
Discussion. When  erected Stipomorpha as a subgenus of Microdon, he did so based on the shape of the abdomen: "...the first two abdominal segments greatly flared and flattened and wider than the thorax; remainder of the abdomen immediately compressed into a rounded, subcylindrical pipe-like form." Shortly after, Hull (1949) ranked Stipomorpha as a subgenus of Paramixogasteroides Shiraki, 1930, without stating a reason for this. Subsequent authors have regarded Stipomorpha as synonymous with Ubristes. See under Ubristes for a discussion on the relationship between these groups, which are here considered as separate genera. Stipomorpha as presently defined contains most species listed under Ubristes by Thompson et al. (1976).
Diversity and distribution. Described species: 16. Descriptions of nine additional species are in preparation by the first author. Neotropical, with records ranging from Costa Rica to Argentina. Description. Body length: 7-9 mm. Broadly built flies with moderately long antennae and short abdomen. Head about as wide as thorax or slightly wider. Face convex; about as wide as an eye. Lateral oral margins distinctly produced. Vertex irregularly swollen. Occiput ventrally narrow, dorsally widened. Eye bare. Eye margins in male converging at level of frons, with mutual distance 2.5 times as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna longer than distance between antennal fossa and anterior oral margin; basoflagellomere about as long as to slightly longer than scape, parallel-sided; bare. Postpronotum bare. Scutellum semicircular; with large, blunt calcars, separated by deep sulcus. Anepisternum weakly sulcate; entirely pilose. Anepimeron entirely pilose. Katepimeron flat; bare. Wing: vein R4+5 with posterior appendix; vein M1 perpendicular to vein R4+5; postero-apical corner of cell r4+5 rectangular, with small appendix; crossvein r-m located around basal 1/4 of cell dm. Abdomen heart-shaped, about as long as wide. Tergites 3 and 4 fused. Sternite 1 bare. Male genitalia: phallus furcate, with furcation point near apex; hypandrium with basal part bulb-like; epandrium without ventrolateral ridge; surstylus deeply furcate.

Diagnosis.
Postpronotum bare. Abdomen about as long as wide, with tergite 2 about as long as tergites 3 and 4 together.
Discussion. The only species included in this group, the Oriental Microdon sulcatus Hull, 1944, does not have any obvious relatives. Because of the bare postpronotum, the rectangular postero-apical corner of cell r4+5, the entirely pilose anepisternum and the characters of the male genitalia, the species does not fit into Microdon s.s.
Diversity and distribution. Described species: 1. Indonesia: Java. The species seems not to be uncommon, as specimens collected by different collectors in different years are present in several entomological collections (BMNH, KBIN, MZH, RMNH, ZMAN). Although entomological collectors have been active in other parts of the Sunda region, such as peninsular Malaysia, Sumatra and Borneo, this species has so far not been found there. This suggests that this singular species is endemic to Java.
Etymology. The generic name is composed of sulcus and odon. The first part means 'furrow' or 'groove' in Latin, but in this case it is derived from Microdon sulcatus, the type species of the genus. The second part of the name is used as a suffix derived from Microdon. Discussion. Reemer (2008) included in his new genus Surimyia a species previously assigned to Paragodon (P. minutula van Doesburg, 1966). Several morphological characters were mentioned to indicate the differences between these genera (Reemer 2008). Especially the structure of the phallus seems fundamentally different: short, straight and unfurcate in Paragodon, and long, curved and bifurcate in Surimyia. Other distinctive differences are the bare postpronotum in Surimyia (pilose in Paragodon) and the bare anatergum in Surimyia (microtrichose in Paragodon).

Surimyia
Diversity and distribution. Described species: 2. Neotropical (presently only known from Surinam). Description. Body length: 8 mm. Moderately slender flies with long antennae and basally constricted abdomen. Face in profile slightly convex, almost straight; laterally weakly depressed, therefore slightly carinate dorsomedially; about as wide as an eye. Lateral oral margins not produced. Frons laterally with round, concave areas, filled with dense golden pile, ventrally delimited by a sharply defined ridge. Vertex irregularly swollen. Occiput narrow ventrally, strongly widened dorsally. Eye bare. Antennal fossa about as high as wide. Antenna longer than distance between antennal fossa and anterior oral margin; basoflagellomere about as long as scape; elongate, with dorsal margin straight and ventral margin convex, apex slightly acute. Postpronotum pilose. Anepisternum with shallow sulcus; entirely long pilose. Anepimeron entirely pilose. Katepimeron weakly convex; bare; with wrinkled texture. Scutellum semicircular, weakly triangular; without calcars. Wing: vein R4+5 with posterior appendix; vein M1 perpendicular to vein R4+5; postero-apical corner of cell r4+5 rectangular, with small appendix; crossvein r-m located around basal 1/7 of cell dm. Abdomen constricted at tergite 1, narrowest at tergite 1, widest at posterior margin of tergite 3. Tergites 3 and 4 not fused, able to articulate independently.

Syrphipogon Hull (subgenus, see
Diagnosis. Frons laterally with round, concave areas, filled with dense golden pile, ventrally delimited by a sharply defined ridge. Transverse suture complete. Tergites 3 and 4 not fused.
Discussion. The only known specimen representing this genus has some characters that are not often found among Microdontinae: mesonotal transverse suture complete, tergites 3 and 4 not fused. The lateral concave and densely golden pilose areas on the frons, which are ventrally delimited by a sharply defined ridge, are even unique within the subfamily. The unfused tergites 3 and 4 may suggest affinity with the Neotropical Ceratophya or the Oriental Kryptopyga, whereas the complete trans-verse suture reminds of Ceratrichomyia and Indascia. However, the specimen does not agree with the diagnoses of any of these genera, so a new genus seems the best way to make sure that this singular taxon will get the attention it deserves in future studies on the taxonomy of Microdontinae. Hopefully, male specimens will be collected in the near future, which can be used for study of the male genitalia and molecular analyses.
Diversity and distribution. Described species: 1. Only known from Costa Rica. Etymology. This genus is dedicated to Dr. F. Christian Thompson, in acknowledgement of the valuable work he has done on the taxonomy of the Syrphidae in general, and the Microdontinae in particular. Description. Body length: 10-11 mm. Slender flies with long antennae and long, brushlike pilosity on hind tibiae. Mimics of Trigona-like stingless bees. Head wider than thorax. Face slightly convex, almost straight in lateral view; wider than eye. Lateral oral margins produced. Vertex flat. Occiput ventrally narrow, dorsally widened. Eye very sparsely and short pilose, appearing bare under low magnification. Eye margins in male converging at level of frons; mutual distance about three times width of antennal fossa. Antennal fossa about as high as wide. Antenna longer than distance between antennal fossa and anterior oral margin; basoflagellomere longer than scape. Postpronotum pilose. Anepisternum sulcate; pilose anteriorly and posteriorly, widely bare in between. Katepimeron convex; bare. Scutellum semicircular; without calcars. Wing: vein R4+5 with posterior appendix; vein M1 perpendicular to vein R4+5; cell r4+5 with postero-apical angle widely rounded; crossvein r-m located between basal 2/5 and 1/2 of cell dm. Hind tibia with long, brushlike pilosity. Abdomen elongate: parallel-sided or somewhat triangular. Tergite 2 with lateral tubercle at half of length. Tergites 3 and 4 fused. Sternites 1, 2 and 3 not separated by very wide membranes. Male genitalia: phallus furcate basally; epandrium with lateral 'fenestrae': well-defined, translucent, oval depressions; surstylus more or less oval. Diagnosis. Hind tibia with long, brush-like pilosity. Scutellum without calcars. Vein R4+5 with appendix. Tergite 2 with lateral tubercle at half of length.

Ubristes
Discussion. Thusfar, Ubristes has been characterized by the brush-like pilosity of the hind tibia, giving the flies the appearance of stingless Trigona-like bees (Cheng andThompson 2008, Thompson et al. 1976). Based on this definition, 31 species were assigned to this group by Thompson et al. (1976), including the type species of Carreramyia, Hypselosyrphus and Stipomorpha. The latter two groups were considered as 'subgroups' of Ubristes by Cheng and Thompson (2008), because the characters previously used to define the groups (abdominal shape) were considered of little taxonomic value.
Closer examination of the morphology reveals several important differences between these taxa. The structure of the male genitalia of Ubristes is very different from those of the species here included in Carreramyia, Hypselosyrphus and Stipomorpha: the phallus is long and slender and furcate near its base, the base of the hypandrium is not bulged and there are well-defined, translucent, oval lateral depressions in the epandrium (here called 'fenestrae'). In external morphology Ubristes is readily distinguished from the mentioned genera by e.g. the lateral tubercles on tergite 2. For other differences see the accounts of the other taxa. Considering the phylogenetic results of Reemer and Ståhls (in press) and the morphological differences between these taxa, Ubristes sensu Thompson et al. (1976) and Cheng and Thompson (2008) is here considered to be polyphyletic, with Carreramyia, Hypselosyrphus and Stipomorpha each as separate lineages. Besides the type species, two undescribed species are assigned to Ubristes. Thompson et al. (1976) and Cheng and Thompson (2008) ranked Ubristes as a subgenus of Microdon. However, the species of Ubristes differ in several characters from the species of Microdon s.s., as defined in the present paper. Here, the view is taken that it is better to treat Ubristes as a genus instead of a subgenus, in order to make sure that Microdon comprises less heterogeneous groups with uncertain affinities.
Diversity and distribution. Described species: 1. Descriptions of two additional species are in preparation by the first author. Central and South America.
Discussion. This species has first been recognized as undescribed by Dr. F.C. Thompson, who is preparing a description of it. As the species posesses some unique characters not found in any other species of Microdontinae, the present authors feel that it belongs in a new genus. These characters are: basoflagellomere strongly widened and more or less triangular; arista pilose; phallus dorsobasally with long projection; epandrium with dorsolateral ridge. Other interesting characters are the undeveloped mouthparts (shared with Masarygus) and the lateral carinae on the face.
Discussion. This species has first been recognized as undescribed by Dr. F.C. Thompson, who is preparing a description of it. This taxon resembles Carreramyia in the bifurcate antenna, the wing venation and the structure of the male genitalia. It differs from that genus by the more or less flat vertex (strongly produced in Carreramyia), the short pilose hind tibia (long pilose in Carreramyia), and the more or less parallelsided, slightly constricted abdomen (triangular in Carreramyia).
Diversity and distribution. Only known from one species, collected in Costa Rica.

Unplaced taxa
A small number of species is left unclassified. These are listed at the end of the following section on species classification. On a few of these taxa, comments are given below.

Microdon sharpii Mik, 1900 Figs 433-434
Discussion. Based on external characters, no close relatives were recovered in the phylogenetic analysis of morphological characters by Reemer and Ståhls (in press). The species is characterized by its metallic blue colouration and golden pilosity, a long basoflagellomere, a medially widely bare face, a rectangular postero-apical corner of wing cell r4+5, and unfused tergites 3 and 4. The latter character may indicate affinity with Ceratophya, Kryptopyga or Thompsodon, but the species lacks other diagnostic characters for these taxa. This species is left unplaced for now.

Nothomicrodon Wheeler, 1924
Discussion. Whether this taxon belongs to Microdontinae or Syrphidae at all is uncertain. It was described from larvae found in an ants nest (Wheeler 1924). Cheng and Thompson (2008) suspect it belongs to another family, perhaps Phoridae. Photographs of a larva can be found at http://syrphidae.lifedesks.org/pages/25523.

Discussion: diagnostic characters of Microdontinae
In order to find diagnostic characters for distinguishing Microdontinae from other Syrphidae, characters described by Hippa and Ståhls (2005), Hull (1949), Shatalkin (1975a, b), Speight (1987) and Thompson (1969Thompson ( , 1972 were evaluated based on the material examined for this study. The discussion of these characters below is subdivided into paragraphs corresponding with the following main body parts: head, thorax, wings, legs, abdomen, male genitalia. Terminology of the aforementioned authors is translated into the terminology used in the present paper (see section Material and Methods). This discussion concludes with a summarizing statement on diagnostic morphological characters of Microdontinae.

Head
The simple, convex face of most Microdontinae has been used as a character for the group by Hull (1949) and Thompson (1969Thompson ( , 1972. A facial tubercle is only found in Eurypterosyrphus. In a few taxa (Ceratrichomyia, Chrysidimyia, Rhopalosyrphus) the ventral part of the face is somewhat bulged, but cannot be considered tuberculate.
The diagnostic value of this character is limited, as the facial tubercle is also missing in several other Syrphidae, e.g. all Pipizini and Eumerini. According to Thompson (1969Thompson ( , 1972, the face of Microdontinae is uniformly pilose. In the present study, however, several taxa were found in which the face is bare medially to varying extent (e.g. species of Rhoga, Schizoceratomyia, Stipomorpha), sometimes even entirely bare (e.g. Masarygus planifrons). Thompson (1972) noted that the anterior oral margin in Microdontinae is not notched. There seems to be some confusion about the interpretation of this character, as Hippa and Ståhls (2005) have coded this character as 'medially notched' for Microdon analis (Macquart, 1842). Apparently, the latter authors have regarded the anterior oral margin as notched when the lateral oral margins are produced. Indeed, these laterally produced oral margins give the impression in anterior view that the anterior oral margin is narrowed (notched). In most other Syrphidae (except Pipizini), however, there is a slight additional narrowing at the extreme anterior part of the oral margin (see e.g. fig. 3 in Speight 1987 and fig. 1A in Hippa and Ståhls 2005). This additional narrowing seems to be correlated with the presence of an anteclypeus. In Microdontinae, no distinction can be made between an anteclypeus and a postclypeus (see below), so this additional narrowing of the anterior margin is not visible. In the present study, we follow Hippa and Ståhls (2005) in the interpretation of this character. Many Microdontinae were found with produced lateral oral margins, as it is in most other Syrphidae, so this character is not considered to be useful for distinguishing the subfamily from other Syrphidae.
According to Speight (1987), Microdontinae possess only one clypeus, whereas an anteclypeus and a postclypeus can be recognized in other Syrphidae. The presence of only one clypeus in Microdontinae can be confirmed based on the present study, but the character has not been studied in other Syrphidae. Speight (1987) mentioned two other characters of the mouthparts he considered to be unique for Microdon: 1. the maxillary sclerites are short, flange-like, oriented transversely rather than longitudinally; 2. the maxillary palps are rudimentary. These characters have not been studied in the present study, and thus cannot be commented upon. In general, the mouthparts of Microdontinae are reduced compared with other Syrphidae. No characters indicating the degree of reduction were included in the present study, but a considerable degree of variation was noticed. In certain taxa, the labella are well-developed and flattened, suggesting a capability of feeding on flat surfaces (e.g. leaves) (this can best be noticed in fresh or alcohol-preserved specimens, as the mouthparts tend to shrivel up when dry). In other taxa, the mouthparts are reduced to such an extent that there is not even an oral opening, indicating these species do not feed at all (Masarygus palmipalpus sp. n., M. planifrons).
Unlike most other Syrphidae, the males are dichoptic (i.e. the eyes do not meet at the top of the head). In the present study, no holoptic Microdontinae were found except for Spheginobaccha chillcotti Thompson, 1974, although in a few taxa the male eyes approach each other quite closely (e.g. Hypselosyrphus). When taken into consideration that dichoptic males also occur in other subfamilies of Syrphidae (e.g. Helophilus Meigen, 1822 and related genera, Neoascia Williston, 1887, Pelecocera Meigen, 1822, this character has limited diagnostic value.
According to Thompson (1969Thompson ( , 1972 the arista of Microdontinae is bare. The only known exception, as found in the present study, is the Australian Undescribed genus #1. As a bare arista also occurs in many other Syrphidae, this character is of limited diagnostic value.

Thorax
A pilose postpronotum has been considered to be an important and stable character for distinguishing Microdontinae (as well as Eristalinae) from Syrphinae (Thompson 1969(Thompson , 1972. In the present study, the postpronotum was found to be pilose in the majority of Microdontinae, but certainly not in all. The postpronotum is bare in several taxa (e.g. Ceriomicrodon petiolatus, Masarygus, Sulcodon, Surimyia, Paramixogaster, Piruwa, Schizoceratomyia). This needs to be taken into account when using keys to genera of Syrphidae in which this character is used (e.g. Thompson 1999).
A few other characters involving the presence or absence of pile on thoracic sclerites have been used. Thompson (1969Thompson ( , 1972 noted that the anterior part of the anepisternum is pilose in Microdontinae, except in Ceriomicrodon petiolatus. In addition, a bare anterior anepisternum was found in an Aristosyrphus sp. n., a Mixogaster sp. n. and in some species of Spheginobaccha. According to Hull (1949) the metasternum is always pilose in Microdontinae. However, this was only true for slightly more than half of the presently studied taxa. The subscutellar hair fringe was absent in all studied Microdontinae (character of Thompson 1969Thompson , 1972. This character also applies to several other Syrphidae (Hippa and Ståhls 2005), so it is not by itself group-defining, although it could be useful in keys.
Another thoracic character considered of importance for Microdontinae (Thompson 1969(Thompson , 1972 is the presence of a complete 'postmetacoxal bridge', formed by the connection of the metapleura. As already observed by Cheng and Thompson (2008), this bridge is lacking in Spheginobaccha. The present study revealed that the metapleura are also distinctly separated in certain species of Rhoga (R. maculata, R. mellea, R. sepul-chrasilva). In two other taxa (Paramixogaster variegata) and Surimyia) the metapleura seem to be touching only in one point, implying an intermediate state for this character. Among other Syrphidae, a complete postmetacoxal bridge is rare, but it is found in e.g. Baccha elongata (Fabricius, 1775), Neoascia Williston, 1886and Sphegina Meigen, 1822(Hippa and Ståhls 2005, and also in Leucopodella Hull, 1949. The well-developed plumule, a plumose posterior extension of the subalar sclerite, is considered to be an important character of Syrphidae. In most Syrphinae and Eristalinae the plumule is usually strongly developed, except in Ceriana Rafinesque, 1815, Sphiximorpha Rondani, 1850, Neoascia, Sphegina, Eosphaerophoria Frey, 1946, Allograpa ventralis (Miller, 1921 and some species of Ocyptamus Ståhls 2005, Speight 1987, X. Mengual pers. comm.). As noticed by Thompson (1969Thompson ( , 1972, Speight (1987) and Hippa and Ståhls (2005), the plumule is strongly reduced in Microdontinae. This is confirmed by the results of the present study, although considerable variation was found. In a few taxa, the plumula is entirely absent (e.g. Carreramyia, Masarygus, Spheginobaccha), while in others a short plumula can be found, with both the length of this sclerite and the microtrichosity varying in length. Speight (1987) drew attention to another character: "At the outer ends of the transverse sulcus of the mesoscutum, Microdon possesses a pair of shelf-like, semi-circular, sclerotized outgrowths of the mesoscutum, which do not seem to have an equivalent in other Syrphids". This apparently indicates the notal wing lamina, which, however, is also well-developed in certain other syrphids besides Microdon, as noted by Hippa and Ståhls (2005). The present data indicate that the notal wing lamina is undeveloped in several Microdontinae, such as Aristosyrphus, Eurypterosyrphus, Masarygus, Paragodon, Rhoga and species of Hypselosyrphus, Indascia and Paramixogaster. A strongly developed notal wing lamina (in the sense of Hippa and Ståhls 2005) was only found in Chrysidimyia. This character has little diagnostic value for the Microdontinae as a subfamily.
As Speight (1987) noticed, the subscutellum (metanotum) is "unusually flat" in Microdon, whereas in many other Syrphidae often a convex plate is present. This character was found to be variable among Microdontinae, but in this group the subscutellum is never as strongly swollen as in several other Syrphidae. However, as many intermediate states occur, this character cannot be used conveniently as diagnostic at the subfamily level.

Wings
The presence of the stigmal crossvein was mentioned as a character of the Microdontinae by Hull (1949) and Thompson (1969). The only exceptions found in the present dataset are Spheginobaccha and Paramicrodon delicatulus Hull, 1937 (the crossvein is present in other studied species of Paramicrodon). A quick but far from exhaustive scan of this character among other Syrphidae learned that the stigmal crossvein is also present in many Eristalinae. Hull (1949) and Thompson (1969) noted that the apical crossveins M1 and dmcu are positioned perpendicular to, respectively, vein R4+5 and vein M in most Mi-crodontinae. Exceptions are Aristosyrphus, Mixogaster, Spheginobaccha, and to a lesser extent Kryptopyga and Schizoceratomyia, in which the anterior 1/3 or 1/2 is directed outward. Among other Syrphidae, perpendicular marginal crossveins can be found in e.g. Neoascia and Ocyptamus Macquart, 1834(subgenus Calostigma Shannon, 1927. In all Microdontinae, as noticed by Thompson (1969), crossvein r-m is positioned basal of the middle of cell dm. This is not an exclusive character of the subfamily, however, as it is shared with all Syrphinae and many Eristalinae.
An apparently universal character for Microdontinae is the basally curved vein R2+3. The first to introduce this character were Hippa and Ståhls (2005), who noted that the only other Syrphidae in which this character is found are the Cerioidini. No exceptions were found in the present dataset. In the present paper, an attempt is made to describe this important character in a way that makes it easier to judge it objectively (Fig. 435).

Legs
The legs of most Microdontinae are marked with clear scars subbasally at the femora and subapically at the tibia, visible as creases surrounding the legs. These scars are named cicatrices, singular cicatrix (Hull 1949, Thompson 1969. In Microdontinae, this character is usually very pronounced, but a few exceptions were found among the studied taxa (e.g. Masarygus palmipalpus, Piruwa phaecada, Schizoceratomyia flavipes). These taxa are small in body size, and cicatrices are present in taxa which are considered closely related (e.g. Schizoceratomyia barretoi). This suggests that the apparent absence of cicatrices might merely be a matter of reduction or reduced visibility of the character. Vague cicatrices can also be seen in several Syrphinae and Eristalinae, although never as clear as in Microdontinae. With these considerations in mind, the character holds a good 'indicating value' for diagnosing the subfamily, but it should be applied with caution. Speight (1987) found that all Syrphidae except Microdon posess a long, bladelike process projecting outwards from the antero-lateral end of the outer side of the posterior mesocoxite, which he termed "trochanteral process of the mesocoxite". This character has not been examined in the present study.

Abdomen
In Microdontinae, four preabdominal segments are found in the male, as has been noted by many previous authors (e.g. Thompson 1969, Hippa andStåhls 2005). This character is shared with the Eristalinae, but constitutes a difference with the Syrphinae. No exceptions were found.
Another abdominal character, noted by Thompson (1969) is the position of the first abdominal spiracle, which is embedded in the metaepimeron in Microdontinae. In the present study, this character was confirmed for most taxa. In a few small taxa the character could not be verified because the spiracle could not be found, neither in the metaepimeron nor in the adjacent membranes. The diagnostic value of this character is limited, as the first abdominal spiracle is also embedded in the metaepimeron in many Syrphinae and Eristalinae (Hippa and Ståhls 2005).

Male genitalia
The last published characterization of genitalia of Microdontinae is the one of Thompson (1969Thompson ( , with some additional notes in 1972. Although since then the understanding of the homologies of Diptera genitalic structures and their terminology has advanced (McAlpine 1981, Sinclair 2000, the characters listed by Thompson (1969) to distinguish Microdontinae from other Syrphidae are still useful. Some of these characters have also been noticed by other authors (Shatalkin 1975a, b, Speight 1987. Most of the singularities of the genitalia of Microdontinae are found in the hypandrium (9th sternum) and its associated structures. The hypandrium itself is a simple structure in Microdontinae, lacking separate lobes.
In most taxa, the hypandrium seems to consist of a basal part and an apical part. In certain species this distinction is very clear, because the basal part is convex in lateral view (e.g. Figs 24, 363, 396), but in other ones these parts are smoothly fused and one needs to look carefully to distinguish them (e.g. Figs 171, 179, 319). However, distinction is possible in most cases because the apical part is usually less sclerotized than the basal part and it is covered with very fine microtrichia, while on the basal part these are lacking. There is no doubt that the basal part is the actual hypandrium, because it articulates with the epandrium basolaterally. Possibly, the apical part is homologous to the gonopods of other Diptera, which are usually simple in Muscomorpha and more or less absent in Syrphoidea (McAlpine 1981). In most Microdontinae the apical part consists of one single structure. If this structure is homologous to the gonopods indeed, then this would imply that the gonopods have become fused. In a few taxa (with a basal position in the phylogeny presented in Reemer and Ståhls in press), the apical part of the hypandrium consists of two separate lobes, e.g. in Aristosyrphus (incl. Eurypterosyrphus), Mixogaster and Spheginobaccha (Figs 29,32,246,387). In these cases it is easier to imagine that these structures are homologous to gonopods. In only one studied taxon, Menidon falcatus, no apical part of the hypandrium seems to be present.
No postgonites (parameres of McAlpine 1981, superior lobes of Metcalf 1921 andStåhls 2005) can be distinguished in Microdontinae, a rare occasion among Diptera according to McAlpine (1981). Hippa and Ståhls (2005) supposed that in this subfamily the parameres are integrated into the phallus, but did not present evidence for this hypothesis.
The phallus (subdivided by Thompson 1969 into ejaculatory duct and ejaculatory hood) is tubular and elongate. Its structure is simple: no separate structures can be recognized, as is possible in other Syrphidae (basiphallus, distiphallus etc.). In most taxa, the basal part (termed 'chitinous box' in Metcalf 1921 andThompson 1969) is swollen and spherical (e.g. Figs 29, 363, 385, 405), but in a few this is not obviously so (Figs 22,386). This basal part might be formed out of the phallapodeme, as Thompson (1974) appears to suggest for Spheginobaccha. However, this seems unlikely, because in other Diptera the phallapodeme does not seem to have a sperm-guiding or -collecting function, while in Microdontinae the spherical base of the phallus clearly has an intermediate position between the sperm duct and the apical part of the phallus. Usually, no external lobes are present, but in some taxa a dorsobasal projection was found (Fig. 22). The aedaegus can be unfurcate or bifurcate. Furcate aedeagi can be divided into a number of types, depending on whether the furcation point is basal or apical, and on the length of the ejaculatory processes (see character nos. 163-165 in Reemer and Ståhls in press).
The phallus, or actually the ejaculatory hood, articulates ventrally with the hypandrium and dorsally with the subepandrial sclerites. The point of articulation with the hypandrium is basal, in contrast with all other Syrphidae. The only studied microdontine taxon in which the phallus was observed to articulate apically with the hypandrium is the African taxon Spheginobaccha guttula Dirickx, 1995, a representative of the perialla-group of Thompson (1974).
Except for the studied African species of Spheginobaccha, S. guttula and S. dexioides Hull, 1944, none of the studied Microdontinae has a clearly recognizable phallapodeme. In the Oriental species of Spheginobaccha this structure is also more or less spherical. According to Thompson (1972), the phallapodeme can be absent or "double" in this subfamily. No explanation is given, but judging from a figure of the genitalia of Microdon manitobensis Curran, 1924 in Thompson and Rotheray (1998) and Vockeroth and Thompson (1987), the phallapodeme in the sense of Thompson corresponds with the dark lines named 'lateral strips' in Reemer and Ståhls (in press,character no. 171). This seems unlikely, because the phallapodeme is a single structure while the lateral strips are paired. Thompson (1969Thompson ( , 1972 pointed out that the ejaculatory apodeme of Microdontinae is 'triangularly flared' apically, except in Paragodon, in which it is not sclerotized. The present study has revealed no other taxa with an unsclerotized ejaculatory apodeme. The shape of this structure was found to be very variable, ranging from elongate, round, trapezoid, triangular, square to rectangular. The ejaculatory sac was found to be sclerotized in all taxa except Paragodon and Surimyia. This structure is also variable in shape.
No characters useful for diagnostic purposes at subfamily level were found in the epandrium and associated structures. The shapes of the cerci and surstyli are highly variable, so much even that it is difficult to use them at generic level.

Summarizing statement
When the characters of Microdontinae described by previous authors are studied across a large set of taxa, as has been done in the present study, exceptions can be found for almost all of them. Characters for which no or few exceptions were found are listed in Table 2. The character of the basal shape of vein R2+3 seems to be the most exclusive external character to separate the subfamily from other Syrphidae. A key to distinguish Microdontinae from other Syrphidae is given below. As not all Syrphidae have been studied, doubtful cases may occur, so it is recommended to verify at least a few of the other characters in Table 2, preferably those of the male genitalia. 1 Vein R2+3 weakly curved basally: angle A < angle B (Fig. 435) Thompson FC (1999) A key to the genera of the flower flies (Diptera: Syrphidae) of the Neotropical region including descriptions of new genera and species and a glossary of taxonomic terms. Contributions on Entomology, International 3: 321-378. Thompson FC (2007)  Archimicrodon-species of the Indo-Australian region (Australia excluded). Archimicrodon boharti (Curran, 1947) (Solomon Islands) differs from this species by the metallic blue shining scutellum, clearly contrasting with the non-metallic mesonotum (in A. malukensis sp. n. mesonotum and scutellum are of the same black colour). The same character also applies to A. limbinervis (de Meijere, 1908) and A. incisuralis (Walker, 1865) from New Guinea, and A. purpurescens (Shiraki, 1963) from Micronesia, which also differ by the black pilose scutellum (white pilose in A. malukensis). Archimicrodon grageti (de Meijere, 1908)  Thorax. Thorax black, except pleurae brownish. Mesoscutum black pilose, except pale yellow pilose along anterior margin, laterally between postpronotum and notopleuron, and in posterolateral corners. Postpronotum pale yellow pilose. Postalar callus black pilose, except pale yellow pilose at posterior apex. Scutellum semicircular, without calcars; entirely pale yellow pilose. Anepisternum with shallow dorsomedian sulcus; white pilose anterodorsally and posterodorsally, widely bare in between. Anterior anepimeron entirely white pilose. Katepimeron sparsely white pilose along dorsal margin, otherwise bare. Katatergum long microtrichose, anatergum short microtrichose. Calypter and halter pale yellow.
Etymology. The specific epithet (adjective) is derived from Maluku, the group of islands to which Halmaheira, where the species was found, belongs. Diagnosis. This species differs from both other known species of Ceratrichomyia by the bare postpronotum and katepimeron, the downward projecting face, and the absence of a ventrolateral ridge on the epandrium.

Ceratrichomyia angolensis
Description (based on holotype). Adult male. Body size: 10 mm. Head. Face occupying approximately 1/2 of head width in frontal view; yellowish brown, except for blackish marks dorsally along eye margin; entirely yellow pilose; with pit-like depressions on dorsal 1/3; face profile more or less straight, strongly produced ventrally below eye margin. Gena yellowish brown. Lateral oral margins not produced. Frons and vertex yellowish brown, a little blackish at and around ocellar triangle; yellow pilose. Occiput yellow; dorsally wide and yellow pilose, ventrally narrow and whitish pilose. Eye bare. Antennal fossa about as wide as high. Antenna orange brown, except basoflagellomere blackish brown; antennal ratio approximately as 6:1:18. Basoflagellomere very long, entirely covered with pile at least as long as 1.5 times diameter of basoflagellomere. Arista very small, shorter than pedicel; situated at about 1/3 from base of basoflagellomere.
Wing: hyaline; microtrichose, except bare on cells bc and c, basal 1/2 of cell r1, almost entirely on cells br, bm, cup and on alula, and posterobasal 1/5 of cell r4+5. Vein bm-cu shorter than basal section of CuA1.
Female unknown. Etymology. The specific epithet (adjective) is derived from Angola, where the species was found. Séguy, 1951  Diagnosis. This species differs from C. angolensis sp. n. by the pilose postpronotum and katepimeron. From C. bullabucca sp. n. it differs by the straight face profile and the parallel-sided tergite 2.

Ceratrichomyia behara
Redescription (based on lectotype). Adult male. Body size: 7 mm. Head. Face occupying approximately 1/2 of head width in frontal view; yellow; entirely yellowish white pilose; depressed on lateral 1/3; face profile more or less straight. Gena yellow. Lateral oral margins not produced. Frons and vertex yellow; yellow pilose. Occiput yellow; dorsally wide and yellow pilose, ventrally narrow and whitish pilose. Eye bare. Antennal fossa about as wide as high. Antenna orange brown, getting dark brown towards apex of basoflagellomere; antennal ratio approximately as 1:0,2:3,5. Basoflagellomere very long, entirely covered with pile at least twice as long as diameter of basoflagellomere. Arista very small, shorter than pedicel.
Wing: hyaline; microtrichose, except bare on cell bc, basally on cell r1 along vein Rs, on most of cell br except microtrichose along vena spuria, on most of cell bm except apical 1/8, basal 1/2 of cell cup. Vein bm-cu shorter than basal section of CuA1.
Abdomen. Constricted at 2nd segment, with tergite 2 parallel-sided, widest at tergite 3 and 4 (slightly wider than thorax). Tergite 1 dark brown; white pilose. Tergite 2 dorsoventrally flattened, dark brown with large, triangular yellow maculae along lateral margin, posteriorly interconnected and reaching posterior margin, which is entirely yellow; white pilose. Tergite 3 and 4 dark brown with yellow posterior margins; white to yellow pilose. Tergite 4 with two faint submedian grooves from anterior margin to just before posterior margin. Sternite 1 yellow; bare. Other sternites brown; white pilose. Genitalia as in Fig. 57.
Female. Unknown. Diagnosis. This species differs from C. angolensis sp. n. by the pilose postpronotum and katepimeron. From C. behara Séguy, 1951 it differs by the convex face profile and the anteriorly widened tergite 2.
Head. Face occupying almost 3/5 of head width in frontal view. Face profile clearly convex.
Wing: cell r1 entirely microtrichose, cell br bare on posterobasal 3/5. Vein bm-cu longer than basal section of CuA1. Abdomen. Tergite 2 not parallel-sided: narrowest point at about half its length; lateral yellow macula, not connected posteriorly. Genitalia as in Fig. 58.
Female. Unknown. Etymology. The specific epithet (noun in apposition) contains the Latin words bulla (bubble, knob) and bucca (cheek) and refers to the swollen face, a character to distinguish the species from C. behara. Diagnosis.Three undescribed species belonging to this genus are known. From those, D. zodiacus sp. n. can be distinguished by the following combination of characters: face with black median vitta, alula entirely microtrichose, tergites 3 and 4 partly yellow.

Domodon zodiacus
Description (based on holotype). Adult male. Body size: 7 mm. Head. Dichoptic. Face occupying about 1/3 of total head width in frontal view; pale yellow with brown median vitta of 1/5 of facial width; entirely yellow pilose; not pollinose; eye margins slightly converging at level of frons, with smallest distance approximately equal to three times width of antennal fossa. Gena black. Oral margin laterally produced; black. Antennal fossa about as wide as high. Frons black with metallic green shine; golden pilose. Vertex convexly produced; shining black; sparsely short pilose. Ocellar triangle not elevated; anterior angle about 100°. Occiput narrow; black; golden yellow pilose dorsally, white pilose ventrally. Eye bare. Antenna dark brown; antennal ratio approximately 4:1:4; basoflagellomere elongate with rounded apex, with small sensory pit located at about 1/3 from base; arista slender, about 2/3 of length of basoflagellomere.
Thorax. Mesoscutum black with faint metallic hues; black pilose, except for a narrow sutural and a wide prescutellar fascia of golden pilosity. Postpronotum blackish; yellow pilose. Postalar callus brown; yellow pilose. Scutellum with two apical calcars of 1/4 of length of scutellum; brown with faint metallic hues. Pleurae blackish brown. Anepisternum with anterior and posterior part separated by clear sulcus; anterior part short black pilose, posterior part long yellow pilose, with bare area in between. Anterior anepimeron entirely pale yellow pilose. Katepisternum yellow pilose dorsally, bare ventrally. Katatergum with long black microtrichia. Anatergum short pale microtrichose. Other pleurites bare. Calypter and halter yellow.
Wing: Hyaline, faintly darker around crossvein r-m; microtrichose, except bare on cell bc, posterobasal 1/2 of cell c, basally on cell r1 along vein Rs, on cell br except along vena spuria and extreme apex, on posterobasal 1/2 of cell bm, on anterobasal 1/2 of cell cup.
Abdomen. Ratio of median tergal lengths approximately as 1:2:3:5. Tergites 3 and 4 not clearly fused, only laterally. Tergite 1 black; pale pilose. Tergite 2 pale yellow with lateral 1/4 black and with posteriomedian black macula; yellow parts yellow pilose, black parts black pilose. Tergite 3 pale yellow with extreme lateral margins black, with sublateral oblique black maculae of slightly less than 1/3 of tergal width, with narrow median black vitta on anterior 2/3; black pilose except yellow pilose along posterior margin. Tergite 4 black except yellow along lateral and posterior margins; black pilose except yellow pilose on yellow parts. Sternite 1 black; bare. Other sternites yellow, sparsely pilose. Genitalia as in 84.
Female. Unknown. Etymology. The name zodiacus (adjective, Greek: 'of animals') was chosen because the type specimen was collected at the Paramaribo Zoo.  Cheng and Thompson (2008) to distinguish Furcantenna Cheng, 2008 from the Neotropical genus Schizoceratomyia Carrera, Lopes & Lane, 1947: scutellum apicomedially sulcate, katepisternum pilose, metasternum developed and pilose. All three characters are found in the species described here. Only one other species of Furcantenna is known (F. yangi Cheng, 2008). From that species, F. nepalensis sp. n. differs by the following characters (characters of F. yangi in parentheses, based on Cheng and Thompson 2008): body colour brownish, without violet shine (black, with violet shine); mesoscutum entirely golden pilose (black and white pilose); katepimeron pilose (bare); tergite 2 with ratio of median length : width of posterior margin approximately as 1:3 (1:6).

Diagnosis. Three characters are mentioned by
Description (based on holotype). Adult male. Body size: 10 mm. Head. Blackish brown. Face occupying about 1/2 of head width in frontal view; laterally depressed and dull, medially with shining carina; white pilose. Gena white pilose. Oral margin not produced. Frons, vertex and occiput golden pilose. Eye bare. Antennal fossa slightly higher than wide. Antenna: scape pale brown, pedicel and basoflagellomere black; antennal ratio approximately as 5:1:17.5; basoflagellomere bifurcate at base, both branches entirely long pilose; arista absent.
Legs: Brown. Front leg golden yellow pilose, except tarsus dorsally black pilose. Mid and hind legs black pilose, except femora largely golden yellow pilose and tarsi ventrally golden pilose. Coxae and trochanters brown; whitish pilose.
Abdomen. Slightly constricted, with narrowest point at posterior margin of tergite 2. Tergite 1 dark brown; yellow pilose. Tergite 2 yellow with dark brown, triangular median macula, with narrowest part at anterior margin and widest part close to posterior margin; yellow pilose, except dark pilose laterally. Tergite 3 yellow with median dark brown vitta and pair of oblique, lateral, dark brown maculae; yellow pilose, except dark pilose on and around lateral dark maculae. Tergite 4 with colour pattern similar to tergite 3, but lateral maculae anteriorly confluent with median vitta; golden yellow pilose, except dark pilose on lateral maculae. Sternites yellow, slightly darkened on sternite 1, 3 and 4; yellow pilose. Male genitalia as in Fig. 94.
Female. As male, except for following differences. Dark maculae on tergite 4 not confluent anteriorly. Tergite 5 yellow with dark brown median vitta and pair of small, round, submedian dark brown spots; golden yellow pilose, except for black pile anteromedially and sublaterally. Sternite 3 dark brown medially. Sternites 4 and 5 dark brown.
Etymology. This species is named after my daughter Doris. The epithet is a noun in apposition. Head. Face occupying about 1/3 of head width in frontal view; black; entirely golden pilose. Gena black; golden pilose. Lateral oral margins produced. Frons black; black pilose, except golden pilose posterolaterally. Vertex black; black pilose, except golden pilose along anterior margin and white pilose along posterior margin. Occiput black; black pilose on dorsal 1/3, white pilose on ventral 2/3. Eye pale pilose, with pile approximately as long as half the diameter of frontal ocellus. Antennal fossa about as high as wide. Antenna brown; antennal ratio approximately as 3:1:2.5.
Legs: Black, except front femur brown anteriorly; white pilose, except golden pilose basoventrally on front and mid femora and apicoventrally on front and mid tibiae, and golden pilose ventrally on tarsi. Coxae and trochanters black; white pilose.
Etymology. This species is named after my partner Elisabeth (Liesbeth) Anna. The epithet is a noun in apposition. Description (based on holotype). Adult male. Body size: 12 mm (paratype 10 mm).

Heliodon tiber
Head. Face occupying about 1/3 of head width in frontal view; black, except brownish yellow on lateral 1/6; entirely white pilose. Gena black; white pilose. Lateral oral margins weakly produced. Frons and vertex black; white pilose. Occiput black; white pilose. Eye pilose, with pile approximately as long as diameter of ocelli. Antennal fossa about as high as wide. Antenna brown; antennal ratio approximately as 3.5:1:2.
Female. As male, except for following differences. Body size 8-12 mm. Overall colouration paler: whereas pale parts are brownish in the examined males, these parts are yellowish in the examined females. The scutellar spines are less strongly developed, and in one of the examined females from Thailand even totally absent.
Etymology. This species is named after my son Tiber. The epithet is a noun in apposition.
Notes. In the paratype and in all additionally studied specimens, the pilosity of thorax and abdomen is more golden yellow than in the holotype, also in the parts which are silvery white in the holotype. In most specimens the legs are entirely yellow, without infuscated parts.
The paratype has a label stating "Microdon fascipennis Sack" (or possibly fuscipennis) in what seems to be the handwriting of J.C.H. De Meijere (judged by comparison with figures of de Meijere's handwriting in De Jong 2000). However, no such name is known to have been given to any Microdontinae, neither by Sack nor by any other author. Either De Meijere was mistaken, or the name is an unpublished manuscript name. Diagnosis. Within Indascia, this exceptionally large species shares the presence of a posterior appendix on vein R4+5 only with I. spathulata sp. n. From that species, I. gigantica differs by tergite 2 being about 1.5 times as long as wide, and the basoflagellomere being 2 times as long as wide.
Head. Face occupying about 1/4 of head width in frontal view; black; entirely silvery white pilose. Gena black, white pilose. Oral margin not produced. Frons and vertex black; golden pilose, except for few black pile at ocellar triangle. Occiput black; yellowish pilose dorsally, white pilose ventrally. Eye bare. Antennal fossa about as high as wide. Antenna black; antennal ratio approximately as 4:1:4.

Female. Unknown.
Etymology. The specific epithet (adjective) refers to the large size of this species in comparison with other known species of Indascia.
Notes. In the holotype, the only specimen available, the posterior appendix of vein R4+5 is composed of two short vein stumps, which are confluent at their apices, forming a triangle with part of vein R4+5. This is unusual, although similar aberrations can be found in single specimens of Microdontinae from different genera and species groups. Whether the venation as found in the holotype is representative of this species remains uncertain. Diagnosis. Within Indascia, this species only shares the presence of an appendix on vein R4+5 with I. gigantica sp. n. From that species, I. spathulata differs by tergite 2 being more than twice as long as wide, and the basoflagellomere being 5 times as long as wide.

Indascia spathulata
Description (based on holotype). Adult male. Body size: 6 mm. Head. Face occupying slightly less than 1/3 of head width in frontal view; black; entirely silvery white pilose. Gena black, white pilose. Oral margin not produced. Frons and vertex black; yellowish white pilose, except for few black pile at ocellar triangle. Occiput black; black pilose dorsally, yellowish pilose laterally and ventrally. Eye bare. Antennal fossa about as high as wide. Antenna black; basoflagellomere with dorsal margin somewhat concave; antennal ratio approximately as 5:1:9.
Wing: Hyaline; microtrichose, except bare on cell sc, basally on cell r1 along vein Rs, basal 1/2 of cell br, basal 3/4 of cell bm, anteriorly on cell cup along vein CuA.
Legs: pale yellow, except blackish brown on basal 1/3 of front, basal 3/4 of mid and most of hind femur (except extreme base and apex yellow in the latter), and distal 2/3 of hind tibia; yellow pilose, except black pilose on 4th and 5th tarsomere of front and mid leg, and on dark parts of hind femur and tibia. Coxae blackish brown; yellow pilose. Trochanters yellow; yellow pilose.
Female. Unknown. Etymology. Even more so than its congenerics, this species has a spoon-shaped abdomen, due to the strongly constricted second segment. This character inspired its name: spathulata (Latin adjective for 'spatulate', spoon-shaped). Diagnosis. This species differs from K. pendulosa by the less modified abdomen: tergite 4 is not perpendicular to tergite 3 and sternite 4 is well visible in ventral view.
Head. Face occupying about 2/5 of head width in frontal view; black on median 1/2, pale brown on lateral 1/4; entirely long appressed yellowish pilose, golden on ventral half. Gena widely developed; blackish; long yellow pilose. Oral margin anteriorly notched, laterally produced. Frons black; short golden pilose. Vertex strongly swollen; black; short golden pilose anteriorly, long black pilose posterior to ocellar triangle. Ocellar triangle not elevated. Occiput strongly swollen dorsally, narrow laterally; black; black pilose dorsally, golden pilose ventrally. Eye bare. Antennal fossa about as high as wide. Antenna blackish brown, scape a little paler basally; ratio of lengths of scape and basoflagellomere approximately as 1:4, pedicel very short; basoflagellomere very long (4 mm), parallel-sided, with very long black pilosity, about 1,5 times as long as width of basoflagellomere. Arista absent.
Thorax. Mesoscutum black; black pilose, except for some golden pile along transverse suture and along lateral margins. Postpronotum and postalar callus brown, black pilose. Scutellum yellow; black pilose. Pleuron blackish brown. Anepisternum with deep sulcus separating posterior from anterior part; mixed yellow and black pilose anteriorly, black pilose posterodorsally, yellow pilose posteriorly. Anepimeron entirely long yellow pilose. Katepisternum long pale yellow pilose dorsally and ventrally.
Wing: hyaline, slightly darkened anteroapically; microtrichose, except bare on 1st and cell c, basal 1/3 of cell r1, basal 1/4 of cell r2, basal 1/2 of cell r4+5, basal 1/2 of cell dm, entirely on cells R and BM, entirely on cell br and BM, anterobasally on cell dm, most of cell cup and most of alula (only microtrichose along margins).
Female. Unknown. Etymology. The specific epithet (noun in the genitive case) is derived from the Indonesian island Sulawesi, the type locality. Diagnosis. This is the only known species of Microdontinae in which the antenna of the male is furcate into five branches.

Masarygus palmipalpus
Description (based on holotype). Adult male. Body size: 4 mm. Head. Head unusually flat. Face wide: occupying about 3/4 of head width in frontal view; somewhat concave laterally; yellow; yellow pilose, except black pilose laterally on dorsal 1/2. Gena yellow; yellow pilose. Oral margin not produced; oral opening barely visible; mouth parts undeveloped. Frons brown; black pilose; very short; distance between frontal ocellus and antennal fossa shorter than height of antennal fossa. Vertex blackish brown medially, yellow laterally; black pilose; ocelli arranged almost in a straight line, with frontal ocellus weakly developed, much smaller than the other two. Occiput yellow; black pilose dorsally, yellow pilose ventrally. Eye bare. Antennal fossa about 1,5 times as wide as high. Antenna black; black pilose; ratio of scape:basoflagellomere approximately as 1:8; pedicel very short. Basoflagellomere furcate into five branches, four of which about equally long, the fifth branches off from one of the other at about ¼ from the base of the segment, with a length of about 2/5 of the other branches. Arista absent.
Wing: Hyaline; microtrichose, except bare on cell sc and basal 1/4 of cell cup. Legs: Front and mid leg pale yellow, except dark brown on basal 3/4; black pilose. Hind leg dark brown, except fifth tarsomere yellow; black pilose. Front coxa exceptionally long: about 4/5 of length of femur, longer than tibia; pale brown; bare. Other coxae and trochanters shorter; pale brown; very sparsely black pilose.
Female. Unknown. Etymology. The specific epithet (noun in apposition) is composed of the Latin words palma (hand) and palpus (feeler, here interpreted as antenna). The name refers to the hand-like antenna of the male of this species. Diagnosis. Distinguished from the other two known (yet undescribed) species of Mermerizon by the black pilose mesoscutum.
Head. Face occupying about 1/4 of head width in frontal view; yellow; yellow pilose, with narrow bare median line on dorsal half. Gena yellow. Frons black; yellow pilose laterally, black pilose posteriorly. Vertex dark yellow, except black at and around ocellar triangle; black pilose. Occiput black, except yellow posteriad of vertex; black pilose on dorsal half, yellow pilose on ventral half. Eye bare. Antennal fossa about as high as wide. Antenna with scape dark brown, pedicel and basoflagellomere yellowish brown; antennal ratio approximately as 4:1:4.
Legs: Front and mid legs yellowish brown; black pilose. Hind leg blackish brown, except basal 1/2 of tibia and apical four tarsomeres yellowish brown. Front and mid coxae and trochanters yellowish brown; yellow pilose apically. Hind coxa and trochanter dark brown; black pilose.
Female. Unknown. Etymology. The specific epithet (noun in apposition) is based on InBio, an acronym of Instituto Nacional de Biodiversidad, the Costa Rican institute which holds the holotype of this species. Description (based on holotype). Adult female. Body size: 13 mm.

Metadon achterbergi
Head. Face occupying about 1/3 of head width in frontal view; dark brown; golden pilose, very narrowly bare medially on ventral half. Gena brown, golden pilose. Lateral oral margin produced. Frons, vertex and occiput brown; golden pilose, except occiput ventrally white pilose. Eye bare. Antennal fossa about as high as wide. Antenna black; antennal ratio approximately as 4:1:3.
Male. Unknown. Etymology. This species is named after its collector, Dr. C. van Achterberg, in acknowledgment of the many ways in which he has been helpful to the senior author during his PhD work. The epithet is a noun in the genitive case. Diagnosis. In the keys of Shiraki (1968), Huo et al. (2007) and -depending on how characters are interpreted - Hironaga and Maruyama (2004), this species keys to M. auricomus Coquillet, 1898, from which it differs by the largely orange legs and the long, orange-golden pilosity on the anterodorsal part of the hind femur. These characters also apply for distinguishing M. hauseri sp. n. from M. murayamai Hironaga & Maruyama, 2004, to which specimens of the species will key in the key of Hironaga & Maruyama (2004). The same characters apply for separating it from Microdon lateus Violovitsh, 1975, to which it keys using Violovitsh (1983. In the key of Shiraki (1930) this species keys to M. formosanus Shiraki, 1930, from which it differs by the black pilosity medially on the mesoscutum (entirely pale in M. formosanus).
Head. Face occupying about 1/3 of head width in frontal view; black; entirely yellowish pilose. Gena black, yellowish pilose. Oral margin not produced. Frons black; black pilose, except narrowly yellow pilose along lateral and posterior margins. Vertex black; black pilose, except narrowly yellow pilose along all margins. Occiput black; yellow pilose. Eye bare. Antennal fossa about as high as wide. Antenna black; antennal ratio approximately as 3.5:1:2.5.

Female. Unknown.
Etymology. This species is named after Martin Hauser, in acknowledgement for the many interesting specimens of Microdontinae he sent to the author. The epithet is a noun in the genitive case. Diagnosis. The orange colouration of large parts of this species' body, most notably its head, legs and the lateral parts of the tergites, precludes confusion with any other known Palaearctic or Oriental species of Microdon s.s.
Head. Face occupying about 1/3 of head width in frontal view; orange yellow; entirely yellow pilose. Gena black, yellow pilose. Oral margin laterally weakly produced. Frons black; yellow pilose. Vertex yellow; yellow pilose. Occiput black; yellow pilose. Eye almost bare, sparse and short pile visible only under high magnification. Antennal fossa about as high as wide. Antenna pale brown; antennal ratio approximately as 3:1:2.5.
Thorax. Mesoscutum blackish bronze with green metallic hues, except yellow along lateral margins; entirely yellow pilose. Postpronotum, postalar callus and scutellum yellow; yellow pilose. Scutellum trapezoid with slightly concave posterior margin; with minute, barely discernable posterolateral calcars, their mutual distance about equal to 1/3 of width of scutellum. Pleuron blackish, except anepisternum anterodorsally with small yellow spot and katatergum medially with small yellow spot; all pilosity yellow. Anepisternum with deep sulcus separating anterior from posterior part; pilose anteriorly and posteriorly, with widely bare part in between. Anepimeron entirely pilose. Katepisternum pilose dorsally; bare ventrally. Katatergum long microtrichose, anatergum short microtrichose. Calypter and halter yellowish white.
Abdomen. Tergite 1 black; yellow pilose. Tergite 2 black, except orange yellow on lateral 1/6; erect yellow pilose , except for fascia of appressed golden pile along posterior margin. Tergite 3 medially with semicircular black mark, anteriorly as wide as the black part on tergite 2, posteriorly narrow and just reaching posterior margin; laterally orange yellow; short black pilose on most of anterior half, except yellow pilose along lateral margins, with fascia of appressed golden pile along posterior margin. Tergite 4 largely orange yellow, except for vaguely defined blackish mark anteromedially; largely short yellow pilose, except for anterolateral patches of black pile. Sternite 1 black; yellow pilose. Sternite 2 and 3 yellow, except blackish near lateral margins; yellow pilose. Sternite 4 yellow; yellow pilose. Male genitalia as in Fig. 213.
Female. As male, except for the following differences. Body size: 14 mm. Frons largely yellow, except for small triangular black area posteriad of lunula. Antenna: scape and pedicel yellowish. Mesoscutum with pair of small submedian yellow spots at posterior margin. Scutellum without any sign of calcars. Anepimeron, dorsal part of katepisternum, katepimeron, katatergum and anatergum yellow. Tergite 4 with fascia of appressed golden pile on posterior half. Tergite 5 largely orange yellow, except blackish anteromedially; entirely appressed golden pilose.
Etymology. The species name (adjective) refers to 'mandarin', which has a number of meanings. It's an orange citrus fruit, it's the most spoken language in China, and it used to be a high governmental function in imperial China. The name is considered appropriate for this species because of the characteristic orange colour of several body parts and the Chinese origin of the type material. Diagnosis. This species keys to Microdon japonicus Yano, 1915 in the keys of Huo et al. (2007) and Shiraki (1930Shiraki ( , 1968. From that species it is distinguished by the entirely yellow pilose mesoscutum (with patches of black pile in M. japonicus). In the key of Hironaga and Maruyama (2004) it keys to M. kidai Hironaga & Maruyama, 2004, from which it differs by its partly yellow legs (entirely black in M. kidai). In the key of Violovitsh (1983) this species keys to M. eggeri Mik, 1897 (= M. analis (Macquart, 1842)), from which it differs by its pale brown scutellum (black in M. analis) and the shape of tergite 2, which is at its widest clearly before the posterior margin (widest at posterior margin in M. analis).
Head. Face occupying a little less than 1/2 of head width in frontal view; black; entirely golden yellow pilose. Gena black, golden yellow pilose. Oral margin not produced. Frons, vertex and occiput black; golden yellow pilose. Eye bare. Antennal fossa about as high as wide. Antenna black; antennal ratio approximately as 2.5:1:1.5.
Thorax. Entire thorax blackish with bronze hues, except scutellum brownish; all pilosity yellow. Scutellum trapezoid with slightly concave posterior margin; with slender calcars as long as 1/5 of length of scutellum, their mutual distance about equal to 1/3 of width of scutellum. Anepisternum with shallow sulcus separating anterior from posterior part; pilose anteriorly and posteriorly, with widely bare part in between. Anepimeron entirely pilose. Katepisternum pilose dorsally and ventrally. Katatergum long microtrichose, anatergum short microtrichose. Calypter and halter yellowish white.
Etymology. This species is named after the Chinese province of Yunnan, in which it was found. The epithet is a noun in the genitive case. Diagnosis. This is the only known species of Paramixogaster with a pair of submedian vittae of golden pilosity on the posterior half of the mesoscutum.
Thorax. Postpronotum yellow; bare. Mesoscutum reddish brown; short yellow pilose, with lateral fasciae of dense golden pile along transverse suture and with two vittae of dense golden pile on posterior half. Postalar callus and scutellum reddish brown; short yellow pilose. Scutellum without calcars. Pleuron reddish brown. Anepisternum with deep sulcus separating anterior and posterior part; white pilose, except with golden pilosity along posterior margin, as an extension of the golden fascia from the mesonotal transverse suture. Anepimeron entirely white pilose. Katepisternum white pilose dorsally; bare ventrally. Katatergum long microtrichose, anatergum short microtrichose. Other pleurites bare. Calypter and halter yellow.
Wing: hyaline; microtrichose, except bare on cell bc, basal 1/2 of cell c, basally on cell r1 along vein Rs, almost entirely on on cells R, BM andl CuP, on alula except along margins.
Male. Unknown. Etymology. The specific epithet (adjective) is derived from the Greek word piptotos (that which has fallen). This name refers to the fact that this species 'fell' out of the genus Ceratrichomyia, for the holotype is also part of the paratype series of Ceratrichomyia behara Séguy, 1951. Notes. This description is based on the female paratype of Ceratrichomyia behara. For discussion see genus account of Ceratrichomyia. Thorax. Black. Mesoscutum short appressed yellowish pilose, except for sparse bristly black pile anterolaterally. Postpronotum bare. Postalar callus black pilose dorsally, pale pilose laterally. Scutellum semicircular; without calcars; black; short pale pilose and with a few long, bristly, pale setae along posterior margin. Anepisternum convex, without sulcus; pale pilose on dorsal half. Katatergum and anatergum short pilose. All other pleurites bare. Calypter grey. Halter yellow with blackish knob.
Legs: Tibiae and femora black. Tarsi whitish yellow, except first tarsomere of hind leg black. Legs black pilose, except tarsi of front and mid leg dorsally yellow pilose. Coxae and trochanters blackish brown. Coxae white pilose apically. Trochanters bare.
Female. As male, except for following differences (based on paratype collected VIII.2009). Face golden yellow pilose. Mesoscutum and scutellum mixed golden yellow and black pilose. Pleuron partly brownish. Anepisternum black pilose dorsally. Anepimeron with bristly black pile along dorsal margin. Coxae apically black pilose. Sternite 5 blackish; short black pilose, withlong, bristly black pile along posterior margin. The other female paratype is apparently a teneral specimen, as parts of its body are yellowish brown.
Etymology. The specific epithet phaecada (adjective) is derived from the Greek word phaikas, which is a kind of white shoe. The name refers to the whitish yellow tarsi of the species that contrast with the entirely black rest of the body. Diagnosis. In three other described Pseudomicrodon species the alula is completely microtrichose: P. chrysostypus (Thompson, 2004), P. pilosops (Marinoni, 2004) and P. smiti sp. n. From these species, P. polistoides sp. n. differs by the entirely orange coloured abdomen, as well as by the yellow median vitta on the mesoscutum. Description (based on holotype). Adult female. Body size: 12.5 mm. Head. Face occupying approximately 1/3 of head width in frontal view; yellow; yellow pilose on lateral 1/3, black pilose on median 1/3. Gena yellow; yellow pilose. Lateral oral margins weakly produced. Frons yellow, except for black markings directly laterad of antennal fossa; yellow pilose, except for sparse black pile at black markings. Vertex yellow, except for black markings at and around ocellar triangle and posterolaterally; bare on anterior 1/3, black pilose on posterior 2/3. Occiput yellow, except black adjacent to black markings on vertex; yellow pilose, except black pilose directly posteriad of vertex. Eye almost bare, with very sparse and short white pile. Antennal fossa about as wide as high. Antenna orange yellow, scape a little darker; antennal ratio approximately as 5:1:6; longer than distance between antennal fossa and anterior oral margin.

Pseudomicrodon polistoides
Thorax. Mesoscutum black with widely yellow margins and wide median yellow vitta over entire length, also narrowly yellow along transverse suture. Black pilose, except for fasciae of orange golden pile along anterior margin, transverse suture and posterior margin, as well as along posterolateral margin. Postpronotum and postalar callus yellow; black pilose. Scutellum semicircular; yellow; black pilose, except sparsely golden pilose anterolaterally; without calcars. Pleuron yellow, except dorsomedial and posterior parts of anepisternum partly blackish, and anatergum and lateral margins of mediotergite blackish. Anepisternum sulcate; mixed orange and black pilose anterodorsally, black pilose posteriorly, widely bare in between. Anepimeron entirely yellow pilose. Katepisternum yellow pilose dorsally, bare ventrally. Katatergum long microtrichose, anatergum short microtrichose. Calypter and halter yellowish white.
Legs: Yellow; yellow pilose, except femora posteriorly black pilose and hind tarsus dorsally black pilose. Front and mid coxae and trochanters yellow; yellow pilose. Hind coxa yellow anteriorly, blackish brown laterally and posteriorly; yellow pilose, except black pilose apically and laterally. Hind trochanter brownish, mixed yellow and black pilose.
Male. Unknown. Etymology. The specific epithet (adjective) emphasizes the resemblance of this species to certain Polistinae (Hymenoptera: Vespidae). Diagnosis. In three other described Pseudomicrodon species the alula is completely microtrichose: P. chrysostypus (Thompson, 2004), P. pilosops (Marinoni, 2004) and P. polistoides sp. n. From these species, P. smiti sp. n. differs by the combination of the black postpronutum and the partly black hind tibia.
Head. Face occupying a little more than 1/4 of head width in frontal view; black, except yellow on lateral 1/5 in dorsal 2/3; entirely yellow pilose; medially with vitta of transversely wrinkled texture. Gena black; yellow pilose. Lateral oral margins weakly produced. Frons black; white pilose. Vertex black; bare on anterior half, black pilose on posterior half. Occiput black; golden pilose on dorsal half, silvery white pilose on ventral half. Eye almost bare, with very sparse and short white pile. Antennal fossa about 1.5 times as wide as high. Antenna black; antennal ratio approximately as 2.5:1:3.5; longer than distance between antennal fossa and anterior oral margin.
Etymology. This species is named after John T. Smit, who collected this species in Peru, along with several other interesting Microdontinae. The epithet is a noun in the genitive case. Diagnosis. In the key of Weems et al. (2003) this species keys to R. australis Thompson, 2003 because tergite 3 is short: a little more than half as long as tergite 2. However, in R. australis tergite 3 is about 1/3 as long as tergite 2, which places R. ecuadoriensis somewhat intermediate between R. australis and the other two known species of Rhopalosyrphus, as far as this character is concerned. Other differences with R. australis are (character state in R. australis in parentheses): antennal ratio approximately as 5:1:8 (5:1:10), mesoscutum almost entirely black pilose (white pilose), tergite 3 black (yellow).

Rhopalosyrphus
Description (based on holotype). Adult male. Body size: 9 mm. Head. Face occupying slightly less than 1/3 of head width in frontal view; black, except yellow on lateral 1/4 on dorsal 2/3; golden yellow pilose, most densely at yellow lateral parts. Gena black, yellow pilose. Lateral oral margins produced. Frons black; yellow pilose. Vertex black; yellow pilose, except black pilose posteriad of ocelli. Occiput black; yellow pilose. Eye bare; with narrow, horizontal area frontally at level of antenna with enlarged ommatidia. Antennal fossa about 1.5 times as wide as high. Antenna black; antennal ratio approximately as 5:1:8; longer than distance between antennal fossa and anterior oral margin.
Legs: Front and mid femora blackish brown, except narrowly yellow at apex; white pilose, except for sparse long, black pile posterodorsally. Front and mid tibiae pale yellow basally, dark yellow apically; white pilose, except for sparse black pile posteroapically. Front and mid tarsi yellow; black pilose dorsally, yellow pilose ventrally. Hind femur black; white pilose anteriorly and dorsally, black pilose posteriorly and with dense, bristly to spiny black pile ventrally. Hind tibia pale yellow on basal 3/5; yellow pilose, except black pilose posteriorly at apical 1/4. Hind tarsus brown; black pilose dorsally, yellow pilose ventrally. Coxae and trochanters brown to blackish; white pilose.
Abdomen. Constricted, about as wide as thorax, with narrowest point just before posterior margin of tergite 2. Tergites black with bronze hues, except tergite 2 yellow along posterior margin. Tergite 1 white pilose, except white pilose on median 1/4. Tergite 2 white pilose, except black pilose dorsomedially on apical 1/2. Tergite 3 white pilose, except for dorsomedian triangle of black pile over entire length, which is widest at posterior margin; white pile posterolaterally thicker and more conspicuous, thus forming a medially interrupted fascia at posterior margin. Tergite 4 black pilose, except white pilose along lateral margins and with fascia of golden yellow pile on posterior 1/3, which is partly interrupted by black pile anteromedially. Sternite 1 dark brown; bare. Sternite 2 brown on anterior 2/3, yellow on posterior 1/3; white pilose. Sternite 3 yellow anteriorly and along posterior margin, brown medially; white pilose. Sternite 4 brown; black pilose, except white pilose along posterior margin. Male genitalia as in Fig. 352.
Female. Unknown. Etymology. The specific epithet (noun in the genitive case) refers to the country where the type has been collected. Diagnosis. Care should be taken in assessing the presence of pile on the katepimeron: in this species this pilosity is very sparse and limited to the anterior margin. Within Rhopalosyrphus s.s. this species is readily distinguished by the pair of large yellow maculae on tergite 2.
Head. Face occupying about 1/4 of head width in frontal view; black, except yellow on lateral 1/6 on dorsal 2/3; entirely silvery white pilose. Gena black, white pilose. Lateral oral margins produced. Frons black; silvery white pilose. Vertex black; black pilose, except white pilose along eye margin. Occiput black; white pilose, except black pilose dorsolaterally. Eye bare; with narrow, horizontal area frontally at level of antenna where ommatidia are separated from each other by wide spaces; the ommatidia present in this area are larger than elsewhere on the eye. Antennal fossa about 1.5 times as wide as high. Antenna black; antennal ratio approximately as 5:1:9; longer than distance between antennal fossa and anterior oral margin.
Legs: Front femur brown dorsally, black ventrally; white pilose, except for sparse black pile posteriorly. Front tibia black, except brown anteriorly on basal 1/4 and apical 1/3; white pilose, except black pilose ventrally. Front tarsus black, except fifth tarsomere brown; yellow pilose. Mid femur black, except brown anteriorly on basal half; white pilose. Mid tibia black, except yellowish on basal 1/6; white pilose. Mid tarsus black on basal three tarsomeres (other tarsomeres missing in holotype); yellow pilose. Hind femur strongly swollen, about 5 times as wide as mid femur; black; white pilose, except sparsely black pilose dorsally and densely occupied with short, bristly, black pile ventrally. Front coxa and trochanter brown; white pilose. Mid coxa black; white pilose. Mid trochanter brown; white pilose. Hind coxa and trochanter black; white pilose.
Abdomen. Constricted, about as wide as thorax, narrowest just before posterior margin of tergite 2. Tergites black with faint metallic hues, except tergite 2 with pair of large, elongate yellow maculae from anterior 1/4 to posterior 1/3. Tergite 1 white pilose. Tergite 2 white pilose, except for patch of black pile dorsally between middle of tergite and posterior 1/6. Tergite 3 black pilose, except narrowly white pilose along posterior and lateral margins. Tergite 4 pilose as tergite 3, but with sparse yellowish pile intermixed among the black pile on posterior 2/3. Tergite 5 mostly yellowish white pilose, with sparse black pile intermixed anteriorly, and colour of pile more whitish near posterior and lateral margins. Sternite 1 brown; white pilose. Sternite 2 yellow; white pilose. Sternite 3 brown; white pilose. Sternite 4 brown; white pilose, on anterior half, mostly black pilose on posterior half, yellowish pilose along posterior margin. Sternite 5 brown; mixed yellowish and black pilose.
Male. Unknown. Etymology. The Latin adjective robustus (strong as oak -Robur) was chosen as the specific epithet because of the size, robustness and stout hind femora of this species, which evoke the impression of a stout fly (strong animal). Diagnosis. Within Rhopalosyrphus s.l. this species is closely related to R. abnormis (Curran, 1925). From that species it differs by the following characters (with character state in R. abnormis in parentheses): eye bare (pilose); antennal ratio approximately as 4:1:9 (2:1:2.5); scutellum without calcars (with calcars); anterior margin of tergite 2 clearly wider than posterior margin (about as wide).

Rhopalosyrphus
Description (based on holotype). Adult male. Body size: 11 mm. Head. Face occupying a little less than 1/3 of head width in frontal view; yellow, with narrow, vaguely defined brown median vitta; entirely golden yellow pilose. Gena black, white pilose. Lateral oral margins produced. Frons black; silvery white pilose. Vertex black; black pilose, except yellow pilose along anterior and lateral margins. Occiput black; black pilose dorsally, golden pilose laterally, silvery white pilose on ventral half. Eye bare; with narrow, horizontal area frontally at level of antenna where ommatidia are separated from each other by wide spaces; the ommatidia present in this area are larger than elsewhere on the eye. Antennal fossa about 1.5 times as wide as high. Antenna black; antennal ratio approximately as 4:1:9; longer than distance between antennal fossa and anterior oral margin.
Legs: Yellow, except hind femur dark brown and hind tibia medially dark brown. Front and mid legs white to yellow pilose, except mid femur dorsally, anteriorly and ventrally black pilose. Hind leg white to yellow pilose, except femur ventrally densely occupied with short, black, bristly pile. Front coxa orange, mid and hind coxae brown; all coxae white pilose. Front and mid trochanters yellow, hind trochanter brown; all trochanters white pilose.
Abdomen. Constricted, narrower than thorax, with narrowest point halfway tergite 2. Tergites brown with faint metallic hues, except tergite 2 with pair of large rectangular yellow maculae on basal 3/5. Tergite 1 white pilose. Tergite 2 yellow pilose, except sparsely black pilose medially and white pilose along posterior margin. Tergite 3 black pilose, except white pilose anterolaterally and along lateral margin, and with fascia of golden pile along posterior margin; this fascia medially interrupted and gradually narrowing towards lateral margins. Tergite 4 black pilose, except golden pilose anterolaterally and along lateral margin, and with pair of large triangular patches of golden pile over posterior 2/3. Sternite 1 brown; bare. Sternite 2 yellow; short yellow pilose. Sternites 3 and 4 brown; white pilose. Male genitalia as in Fig. 353.
Female. Unknown. Etymology. The name abnormoides (adjective) was chosen to underline the similarity of this species to Microdon abnormis Curran. Diagnosis. Within Rhopalosyrphus s.l. this species is singular because of its short antenna (slightly shorter than distance between antennal fossa and anterior oral margin) and the shape of the ventral part of the face.
Head. Face occupying a little more than 1/3 of head width in frontal view; black; entirely white pilose; ventral part of face anteriad of oral margin with lateral bulges, medially separated by shallow, smooth sulcus. Gena black, white pilose. Lateral oral margins slightly produced. Frons, vertex and occiput black; white pilose, except for sparse black pile on frons. Eye bare. Antennal fossa about as high as wide. Antenna brown; antennal ratio approximately as 4:1:3; slightly shorter than distance between antennal fossa and anterior oral margin.
Legs: Front and mid legs orange brown, except mid femur blackish brown on basal 2/5; white pilose, except front tibia black pilose on apicodorsal 1/4, tarsi dorsally black pilose and mid femur on apical 1/2 posterodorsally with sparse bristle-like pile among long white pile. Hind leg black, except basal 1/2 of tibia and apical four tarsomeres dark brown; white pilose, except tarsus dorsally black pilose and femur on apical 1/5 with row of short, black, bristle-like pile anteroventrally; femur swollen: about 2.5 times as wide as mid femur. Front coxa brown, mid and hind coxae black; all coxae white pilose. Front and mid trochanters brown, hind trochanter black; all trochanters white pilose.
Female. Unknown. Etymology. The specific epithet (noun in the genitive case) is composed of the Greek oreos (mountain) and Kaw, the name of the French Guyanan mountain region in which the species was found.
Notes. This species is very aberrant from other known species of Rhopalosyrphus because of the short antenna, the straight facial profile, the bare katepisternum and the long and slender second abdominal segment. These characters suggest that the species may not belong in Rhopalosyrphus. However, it is certainly related to that genus, considering the structure of the male genitalia and the constricted abdomen. If a new genus were to be erected for this species, more evidence on its phylogenetic affinities to Rhopalosyrphus and other related genera (e.g. Pseudomicrodon) should be available. Description (based on holotype). Adult male. Body size: 8 mm.

Thompsodon conspicillifrons
Head. Face occupying about 1/3 of head width in frontal view; yellow with black median vitta, which is dorsally about as wide as the antennal fossa and gradually narrows downward, becoming absent in ventral 1/4; yellow pilose, except for sparse black pile submedially, narrowly bare medially. Gena blackish; yellow pilose. Lateral oral margins not produced. Frons black; golden pilose; laterally with round, concave areas, filled with dense golden pile, ventrally delimited by a sharply defined ridge. Vertex irregularly swollen; black; short golden pilose. Ocellar triangle not elevated. Occiput narrow ventrally, strongly widened dorsally; black; golden pilose. Eye bare. Antennal fossa about as high as wide. Antenna with scape pale brown, pedicel and basoflagellomere blackish brown; antennal ratio approximately as 4:1:4. Thorax. Mesoscutum black; golden pilose, except for pair of black pilose patches anteriad of transverse suture and wide fascia of black pile posteriad of transverse suture. Postpronotum and postalar callus brown, golden pilose. Scutellum black; golden pilose. Pleuron yellowish brown, except anepisternum and anepimerond blackish. Anepisternum with deep sulcus separating posterior from anterior part; entirely mixed yellow and black pilose. Anepimeron entirely mixed yellow and black pilose. Katepisternum long yellow pilose dorsally, bare ventrally. Katatergum short microtrichose, anatergum bare. Calypter dark greyish. Halter yellow.
Abdomen. More or less oval, but tergite 1 very narrow, so appears constricted basally. Tergites 3 and 4 not fused, able to articulate independently. Tergites blackish. Tergite 1 yellow pilose. Tergite 2 short black pilose, with medially interrupted fascia of longer golden pile along posterior margin. Tergite 3 with similar pattern of pile as tergite 2, but fascia of golden pile medially strongly extended over median part of tergite. Tergite 4 largely golden pilose, except for narrow median vitta of black pile and sublateral oblique vittae of black pile. Tergite 5 golden pilose. Sternites black. Sternite 1 bare, other sternites golden pilose.
Male. Unknown. Etymology. The specific epithet (noun in apposition) is composed of the Latin words conspicillum (spectacles) and frons (forehead). The name refers to the concave lateral areas on the frons which (in the eyes of susceptible beholders) evoke the impression of glasses on a forehead.
Notes. This species was first recognized as an undescribed taxon by F.C. Thompson, who gave it the preliminary code-name Microdon MCR-12.

Appendix 2. Species classification of Microdontinae
In total, 552 species group names (excluding misspellings) applying to Microdontinae are currently known, including 98 synonyms and 26 species described in the present paper. Based on the generic diagnoses and discussions in the preceding section of this paper, the classification of all but a few of these species is re-evaluated. This has resulted in a new species classification, partly based on examination of type material. Primary types (or, in seven of these cases, photographic images of those) of 347 specific taxa were examined. In addition, the classification of six species is based on paratypes. In several cases, no type material was examined, e.g. in the case of well-known taxa from temperate regions, in the case of groups that have been revised by other authors (Mixogaster, Spheginobaccha), in the case of recently described species of which good illustrations are available, and in cases of species of which the types could not be found. For these cases, original descriptions, additional material and literature have been consulted. For each taxon, the source of the information on which the classification was based is indicated (for legend see below *: An asterisk denotes information which supplements or corrects information in Systema Dipterorum (Thompson 2010). Acronyms for type information follow Systema Dipterorum (Thompson 2010): KIND_OF_TYPE: HT = holotype; LT = lectotype; NT = neotype; ST = syntype(s); T = unspecified. SEX/STAGE: A = adult; F = female; L = larva; M = male; P = puparium.