A revision of the shore-fly genus Hydrochasma Hendel (Diptera, Ephydridae)

Abstract A revision of the shore-fly genus Hydrochasma Hendel. The species of the genus Hydrochasma Hendel are revised, including 27 new species (type locality in parenthesis): H. andeum (Ecuador. Guayas: Boliche (02°07.7'S, 79°35.5'W)), H. annae (United States. Utah. Grand: Swasey Beach (15.3 km N Green River; 39°07'N, 110°06.6'W; Green River; 1255 m)), H. capsum (Ecuador. Orellana: RíoTiputini (0°38.2'S, 76°8.9'W)), H. castilloi (Ecuador. Loja: Catamayo (03°59'S, 79°21'W)), H. crenulum (Peru. Cuzco: Paucartambo, Atalaya (Río Alto Madre de Dios; 12°53.3'S, 71°21.6'W; 600 m)), H. denticum (Ecuador. Orellana: Río Tiputini (0°38.2'S, 76°8.9'W)), H. digitatum (Peru. Madre de Dios: Diamante (Río Alto Madre de Dios; 12°19.9'S, 70°57.5'W; 400 m)), H. distinctum (Costa Rica. Limón: Parque Nacional Barbilla, Sector Casas Negras, (10°0.8'N, 83°28.1'W; 300 m)), H. dolabrutum (Dominican Republic. Barahona: Barahona (18°12'N, 71°5.3'W)), H. edmistoni (Dominican Republic. Azua: near Pueblo Viejo (18°24.8'N, 70°44.7'W)), H. falcatum (Peru. Madre de Dios: Río Manu, Erika (near Salvación; 12°50.7'S, 71°23.3'W; 550 m)), H. glochium (Dominican Republic. Peravia: San José Ocoa (10 km NE; 18°35'N, 70°25.6'W)), H. kaieteur (Guyana. Kaieteur Falls (05°10.5'N, 59°26.9'W)), H. lineatum (Trinidad and Tobago. Trinidad. St. George: Filette (1 km SE; 10°47'N, 61°21'W)), H. miguelito (Honduras. Cortés: San Pedro Sula (8 km S; 15°25.7'N, 88°01.4'W)), H. octogonum (Ecuador. Manabí: Pichincha (01°02.7'S, 79°49.2'W)), H. parallelum (Trinidad and Tobago. Trinidad. St. Andrew: Lower Manzanilla (16 km S; 10°22'N, 61°01'W)), H. peniculum (Dominican Republic. Pedernales: Pedernales (18°01.8'N, 71°44.7'W)), H. rictum (Honduras. Cortés: San Pedro Sula (8 km S; 15°25.7'N, 88°01.4'W)), H. robustum (Brazil. São Paulo. Ubatuba, Praia Puruba (23°21'S, 44°55.6'W; beach)), H. sagittarium (Trinidad and Tobago. Tobago: St. John: Parlatuvier (creek; 11°17.9'N, 60°35'W)), H. simplicum (Costa Rica. Limón: Parque Nacional Barbilla, Sector Casas Negras, (10°01.2'N, 83°26.2'W; 300 m)), H. sinuatum (Belize. Stann Creek: Mullins Creek (17 km N Dangriga; 17°06.2'N, 88°17.8'W)), H. spinosum (Costa Rica. Limón: Westfalia (4 km S; 09°54.5'N, 82°59'W; beach)), H. urnulum (Dominican Republic. Puerto Plata: Río Camu (14 km E Puerto Plata; 19°41.9'N, 70°37.5'W)), H. viridum (Guyana. Karanambo, Rupununi River (ox bow; 03°45.1'N, 59°18.6'W)), H. williamsae (Belize. Stann Creek: Mullins River (17 km N Dangriga; 17°06.2'N, 88°17.8'W)). All known species are described with an emphasis on structures of the male terminalia, which are fully illustrated. Detailed locality data and distribution maps for all species are provided. A lectotype is designated for Discocerina incisum Coquillett and Hydrochasma zernyi Hendel. For perspective and to facilitate genus-group and species-group recognition, the tribe Discocerinini is diagnosed and a key to included genera in the New World is provided.


Introduction
Hydrochasma Hendel is one of three genera of the shore-fly tribe Discocerinini (subfamily Gymnomyzinae) that occurs exclusively in the New World. The other two Discocerine genera are Pectinifer Cresson, which is known only by its genotype, P. aeneus Cresson, and Facitrichophora Mathis & Zatwarnicki, which was recently described and includes four Neotropical species (Mathis and Zatwarnicki 2012a). Within Discocerinini, Pectinifer is placed in the Diclasiopa group of genera, and Hydrochasma, like Facitrichophora, is classified in the Discocerina group of genera (Zatwarnicki and Mathis 2001). Among all New World genera of Discocerinini, Hydrochasma is perhaps the least well known, as indicated by the dramatic increase in recognized species reported in this revision. Until this revision, Hydrochasma included just seven species (Mathis and Zatwarnicki 1995 and updates), and in this revision, we more than quadruple that number by adding 27 previously undescribed species. These additions bring the total number of congeners to 34.
We are revising the biologically diverse Hydrochasma to account taxonomically for numerous undescribed species that we have collected and recently discovered. Much of this rather dramatic increase has resulted from a greatly improved sampling of the New World fauna, especially the Neotropical fauna where the first author has focused his fieldwork for nearly four decades. Also contributing to this increase is our use of characters from structures of the male terminalia, which has revealed species complexes for what had been treated in some cases as a single, widespread species. The species of the incisum or leucoproctum groups are examples of this discovery process.
Although specimens are not generally uncommon in nature, most collections, with few exceptions, have relatively few specimens, and the genus is not generally well known except to specialists. Only a few authors have reported on any included species, and aside from Cresson (1938Cresson ( , 1942Cresson ( , 1946, there are no comprehensive treatments available. The literature on included taxa is not extensive and mostly comprises alphalevel taxonomic treatments, sometimes as isolated species descriptions. In view of recent field work and discovery of numerous undescribed species, the available literature is also inadequate for dealing with species that are found only in the New World. We also know virtually nothing about the ecology and natural history of any of the included species except for brief habitat characterizations where adults have been found (Deonier 1965). With clarification of species-how they can be recognized and where they occur -we hope that additional research on immature stages and other aspects of their natural history and ecology will be fostered and facilitated. Hendel (1936) first described Hydrochasma with Hydrochasma zernyi Hendel (= Discocerina faciale Williston) as its genotype by monotypy. Cresson (1938, 1946Neotropical, 1942 published brief synopses of New World species, and in the first synopsis, he included the description of H. capax (= H. faciale) and H. patens. Before Hendel (1936), however, the first four species now placed in Hydrochasma were all initially described in the genus Discocerina: H. leucoproctum (Loew 1861), H. faciale (Williston 1896), H. incisum (Coquillett 1902), and H. poecilogastrum (Hendel 1930 = H. incisum). Aside from these isolated species descriptions, recent catalog entries (Wirth 1965Nearctic, 1968Neotropical, Mathis and Zatwarnicki 1995 and faunistic listings Stone 1956 California, Cole 1969 Western North America), the species of Hydrochasma have essentially not been treated. We (Mathis and Zatwarnicki 2010) described three species, H. aquia, H. avanae, and H. garvinorum, as part of a faunistic treatment of the mid-Atlantic shore-fly fauna of the United States.
Even though there is a paucity of taxonomic information on species of Hydrochasma, we know even less about the natural history of any included species. Deonier (1964Deonier ( , 1965 recorded his observations that specimens of H. leucoproctum (as D. leucoprocta) were a common species on sandy shores in Iowa, but only occasional on limnic wrack, and were rare in sedge meadow and marsh reed habitats.

Methods and materials
The descriptive terminology, with the exceptions noted in Mathis (1986) and Mathis and Zatwarnicki (1990a), follows McAlpine (1981). Because specimens are small, usually less than 2.60 mm in length, study and illustration of the male terminalia required use of a compound microscope. We have followed the terminology for most structures of the male terminalia that other workers in Ephydridae have used (references in Mathis 1986;Zatwarnicki 1990a, 1990b), such as surstylus. Zatwarnicki (1996) suggested that the pre-and postsurstylus correspond with the pre-and postgonostylus and that the subepandrial sclerite is the same as the medandrium. The terminology for structures of the male terminalia is provided directly on Figs 2-5. We use the term basal flagellomere for the large antennomere beyond the pedicel. We prefer this term over "first flagellomere" as there may be more than one flagellomere involved, and basal does not imply a number or numbers. We likewise do not use "postpedicel" (Stuckenberg 1999) for this antennomere because at least the multisegmented arista is beyond the pedicel in addition to the large antennomere, and postpedicel is thus ambiguous and lacking in precision.
Dissections of male terminalia were performed following Clausen and Cook (1971) and Grimaldi (1987). Abdomens were removed with microforceps and macerated in a sodium hydroxide solution. Cleared genitalia were then transferred to glycerin for observation, description, and illustration. The dissected abdomen was placed in a plastic microvial filled with glycerin and attached to the pin supporting the remainder of the insect from which it was removed. These structures for species of Hydrochasma are minute, and for accurate determinations using them, we often had to use a compound microscope to see them clearly.
The species descriptions are composite and not based solely on holotypes. Head and two venational ratios used in the descriptions are based on three specimens (largest, smallest, and one other): gena-to-eye ratio -genal height (immediately below maximum eye height)/eye height; costal vein ratio -the straight line distance between the apices of R 2+3 and R 4+5 /distance between the apices of R 1 and R 2+3 ; M vein ratio -the straight line distance along vein M between crossveins dm-cu and r-m/distance apicad of dm-cu.
Distribution maps were made using ESRI ArcView© GIS 3.2. Longitude and latitude coordinates were obtained for the locality where each specimen was collected and entered into a Microsoft Excel© spreadsheet. If unavailable directly from specimen labels, longitude and latitude were estimated using gazetteers and maps to determine the geographical coordinates. Localities of specimens were plotted on a world land projection, presented within ESRI ArcView layouts and exported as encapsulated postscript (EPS) files.
Many specimens examined for this study are in the National Museum of Natural History, Smithsonian Institution, Washington, D.C. (USNM). We also borrowed and studied numerous specimens, especially primary types from the following museums: deagus, associated with hypandrium and with ventral part of base of aedeagus, ventral margin with lobate appendix providing attachment for genital muscles that move aedeagus, sometimes fused with base of aedeagus; gonites paired, connecting sides of base of aedeagus and laterodorsal margin of epandrium, bearing 1 or some setulae; subepandrial plate reduced; aedeagus tubular, tapered anteriorly; ejaculatory apodeme usually lacking, if present as a spatula-shaped structure against background of ductus ejaculatorius.
Discussion. Starting with Cresson (1925), who first described Discocerinini, and including all students of the family until Mathis and Zuyin (1989), the diagnoses, descriptions, and catalogs of this tribe included some taxa that are not closely related phylogenetically, rendering the tribe polyphyletic. Mathis and Zuyin (1989) recharacterized Discocerinini using synapomorphies and resulting in a monophyletic tribe into which Mathis and Zatwarnicki (1995) included eight genera and 143 species in their world catalog. Zatwarnicki and Mathis (2001) then added two additional genera, Galaterina and Orasiopa, and altered the status of some subgenera in their phylogenetic study of the tribe. Finally, Mathis and Zatwarnicki (2012a) recently described Facitrichophora.
Phylogenetic relationships. On a world basis, Zatwarnicki and Mathis (2001) proposed a phylogenetic hypothesis for the higher-level lineages within the tribe Discocerinini, dividing the included genera into three sublineages or groups: the Gymnoclasiopa, Diclasiopa, and Discocerina groups. Hydrochasma is included in the Discocerina group and is distinguished from other New World genera in the key and generic diagnosis that follow (characters being discussed are synapomorphies unless otherwise specified). Other genera in addition to Hydrochasma that are included in the Discocerina sublineage are: Discocerina Macquart, Facitrichophora Mathis & Zatwarnicki, Galaterina Zatwarnicki & Mathis, Lamproclasiopa Hendel, Orasiopa Zatwarnicki & Mathis, and Polytrichophora Cresson. Hydrochasma, along with other genera of the Discocerina sublineage, form a monophyletic lineage within the Discocerinini that is corroborated by two synapomorphies. The first is the setulose notopleuron. In other genera of the subfamily Gymnomyzinae, including other genera in the tribe Discocerinini, the notopleuron is bare except for larger anterior and posterior setae that are inserted near the ventral margin. In taxa of the Discocerina group, however, the notopleuron bears a few additional setulae that are usually inserted slightly dorsad and toward the anterior portion of the notopleuron, usually around or just dorsad of the anterior notopleural seta. The second synapomorphy confirming the monophyly of the Discocerina group is the shape of the gonite, which is narrowly bar-like, often nearly parallel sided. In other genera of Discocerinini outside of the Discocerina group, the gonite is elongate, variously swollen medially, and tapered toward one or both apices. Within the Discocerina group, an elongated male terminalia (hypopygium), at least 2.5× longer than wide (the plesiomorphic condition is hypopygium of moderate length), occurs almost exclusively in four genera: Facitrichophora, Galaterina, Hydrochasma, and Polytrichophora. The genera Facitrichophora, Hydrochasma and Polytrichophora are characterized by a deeply incised posterior margin of hypandrium (the plesiomorphic condition is for the hypandrium to have a slightly to moderately concave posterior margin). Within the Discocerina group, Hydrochasma is distinguished by the following synapomorphies: (1) three facial setae (by convergence, some species in related genera also have three setae); (2) parafacial setulose (a species group within Discocerina also has a setulose parafacial, apparently by convergence); (3) gena high (the buccata species group within Discocerina also has a high gena); (4) cerci usually fused ventrally or ventrolaterally with epandrium (the cerci are similarly fused in many species of Facitrichophora and Polytrichophora); (5) epandrium with dorsal portion or arch above the cerci weakened, thin, or absent; (6) posterior margin of hypandrium deeply incised.
Face distinctly prominent at level of dorsal facial seta; antennal grooves generally sharply defined ventrally; face lacking secondary series of setae; facial setae 3, sometimes with a smaller 4th seta ventrally, setae generally decreasing in size from dorsum to venter, aligned vertically in a single series, dorsal setae not arising from shiny papilla, lacking an dorsoclinate seta at ventrolateral extremity; parafacial moderately wide to wide, expanded posteroventrally, bearing setulae; gena generally high, although variable. Eye generally oval with slight anteromedial expansion, moderately conspicuously microsetulose, bearing distinct interfacetal setulae. Maxillary palpus yellow apically. Thorax: Single presutural and postsutural supra-alar setae well developed; acrostichal setae present; notopleuron bearing several setulae in addition to 2 larger setae; anterior notopleural seta inserted conspicuously closer to posterior notopleural seta than to postpronotal seta. Wings transparent, shiny; costa bearing 4-6 long, dorsal setae between humeral and subcostal breaks. Hindtibia lacking or bearing a preapical, ventral, spur-like seta. Abdomen: Tergites variable, unicolorous or bicolorous, often with lighter colored areas laterally, sometimes as lateral wedges (Figs 12,(70)(71)(142)(143)(184)(185). Male tergite 4 only slightly longer than tergite 3. Male terminalia: Epandrium generally elongate, dorsal portion above cerci weakly developed or usually not connected, with a dorsal gap; mid and posterior surface mostly covered with setae; cercus separate or fused ventrolaterally or ventrally with epandrium, in posterior view broadly lunate; gonite symmetrical, separate from hypandrium, bar-like, situated between base of aedeagus and posterior margin of hypandrium, lacking seta; aedeagus symmetrical, mostly tubular, sometimes very elongate, in ventral view elongate, often cigar-like, in lateral view slightly sinuous with rounded or expanded apex, rarely with dorsal projection; hypandrium in ventral view U-or V-shaped, sometimes narrow, with rounded or variously incised anterior margin, in lateral view almost flat or slightly arched; aedeagal apodeme separate from aedeagus, in lateral view elongate with variable ventral projection, usually small; ejaculatory apodeme absent. Distribution. Specimens of Hydrochasma have thus far been found only in the New World, occurring where temperate and tropical climates prevail.
Natural history. Adults of Hydrochasma occur on bare, often exposed mud and sand, and many species abound in estuarine habitats, especially those along maritime coasts. Specimens are also common in inland alkaline and saline habitats. The immature stages are unknown.
Discussion. Hydrochasma is usually readily recognized. For a few of the included species, however, determining generic assignment can be difficult because external characters are not always wholly concordant with interpretations of structures of the male terminalia (see species excluded near the end of this paper, p. 150). Diagnosis. This species group is distinguished from others within Hydrochasma by the following combination of characters: Head: Subglobose; oral opening large, often gaping. Thorax: Hindtibia with prominent, spur-like, ventral, subapical seta. Abdomen: Tergites without sharply demarcated lateral line or lateral wedges, although darker dorsomedially than on lateral margins. Male terminalia: Ventral epandrial extensions usually relatively wide, if narrow, then tapered to apex; ventral margin of epandrium bifurcate, often deeply.

Key to species groups of Hydrochasma Hendel
Key to species of the faciale group 1 Oral opening comparatively small (Fig. 1); base of epandrium almost as wide as epandrial length (Fig. 57); hypandrium in lateral view deep, pocket-like (Fig. 60) Cresson 4 Ventral epandrial extensions elongate, very slender, parallel sided (Figs 13,Ventral epandrial extensions moderately slender, tapered, not parallel sided .... 6 5 Base of epandrial process in lateral view with incised notch (Fig. 40)  Epandrial extensions in lateral view ( Fig. 3) with apical portion tapered to narrowly rounded point; hypandrium in ventral view with anterior margin as an arrow head (Fig. 4)  Distribution (Fig. 6). Neotropical: Ecuador (El Oro, Guayas, Loja). Etymology. The specific epithet, castilloi, is a genitive patronym to honor Roberto Levi-Castillo, the collector of the type series and many other shore flies from Ecuador.
Remarks. This species has been frequently misidentified as H. patens in collections. Our study of the holotype of H. patens, however, reveals it to be a separate and distinct, although closely related species. Fortunately, the structures of the male terminalia are very diagnostic and distinctive. These structures in H. castilloi are generally much more robust and shorter in both posterior and lateral views . In addition, the aedeagus in lateral view (Fig. 5) is shallowly sinuous, and the hypandrium in ventral view ( Fig. 4) has much shorter, posterolateral processes. In H. patens, the aedeagus in lateral view is shallowly arched, not sinuous, and the posterolateral hypandrial processes are three to four times longer than those of H. castilloi. In general form, structures of the male terminalia of this species are more similar to those of H. faciale and H. williamsae, being relatively short and robustly developed. The dorsum of the epandrium in H. castilloi is complete though thinly developed; whereas in H. faciale and H. williamsae, the dorsal band is incomplete resulting in an open dorsal margin to the cercal cavity.
Remarks. The shapes of structures of the male terminalia of H. crenulum are unmistakable and readily distinguish this species from congeners, especially those of the faciale group. This is especially evident in the ventral portion of the epandrium in lateral view that is generally robustly developed, is conspicuously and widely notched, and terminates as an extended, curved process.

Hydrochasma digitatum sp. n.
http://zoobank.org/8F13EFB9-BD3E-4EC4-B1CF-66A3A8F1FC18 http://species-id.net/wiki/Hydrochasma_digitatum  Diagnosis. This species is distinguished from other congeners by the following combination of characters: Small shore flies, body length 1.40-1.90 mm. Head: Antenna mostly dark gray; parafacial silvery white, concolorous with facial coloration; genato-eye ratio 0. 15-0.17 ing lighter gray laterally but unevenly, almost shallowly wedge-like, tergite 5 of male gray with a thin, medial brown stripe (Fig. 12). Male terminalia : Combined structures generally moderately elongate, in posterior view height over 2× width, generally setulose on cerci, setulae sparse or minute ventrally; epandrium with dorsal arch above cerci not interrupted, narrowly connected, in posterior view ( Fig. 13) with basal ½ somewhat rectangular with angles rounded, apical ½ narrowed, extended as separate, narrow, almost parallel sided processes with a deep and moderately wide gap between processes, lateral margins very shallowly arched, each process rounded apically, in lateral view (Fig. 14) generally shallowly arched with curvature relatively even, widest just ventrad of cercus, apical third abruptly narrowed, tapered, curved anteriorly subapically, apex narrowly rounded, bearing minute setulae; aedeagus in lateral view ( Fig. 16) elongate, narrow, irregularly tubular, shallowly curved, gradually tapered on basal ¾, thereafter widened to form a boxlike apex (angles rounded), in ventral view ( Fig. 15) mostly parallel sided on basal ⅔, apical ⅓ more narrowed but still parallel sided, apex rounded; phallapodeme in lateral view ( Fig. 16) oriented perpendicular to aedeagus, narrowly elongate, keel very evident as an extension on portion toward hypandrium, portion toward aedeagal base rod-like in ventral view (Fig. 15) as a short, rounded, isosceles triangle with a circular structure at base, foreshortened; gonite in lateral view ( Fig. 16) rod-like, straight, narrow, in ventral view ( Fig. 15) short due to foreshortening; hypandrium in lateral view ( Fig. 16) elongate, comparatively wide, anterior margin narrowly rounded, posterior margin as 2 narrow, elongate processes, which form a deep gap between, posterior projection acutely pointed and shorter than anterior projection, in ventral view ( Fig. 15) as an arrowhead that is deeply incised posterolaterally with a tapered, elongate, acutely pointed, posterolateral projection, base extended posteriorly, parallel sided along middle portion, thereafter flared posterolaterally as 2 symmetrical processes, forming a wide, V-shaped posterior margin.  arch above cerci attenuated, not connected, in posterior view ( Fig. 21) with cercal cavity forming a U, with arms of U robustly developed, ventral portion with each lateral half robustly developed, tapered to ventral apex, apex pointed, deeply and narrowly incised medially, medial incision 3× longer than wide, widest at apex, in lateral view ( Fig. 22) with ventral portion robust, apex obtusely pointed; cerci moderately long, height more than twice width, widely semi-hemispherical (Fig. 21), pointed dorsally, not attached lateroventrally or ventrally with epandrium; aedeagus in lateral view ( Fig.  24) elongate, almost 4× longer than width, tubular, shallowly curved, apex rounded, in ventral view (Fig. 23) mostly tapered from base to pointed apex, apical third more abruptly tapered; phallapodeme in lateral view (Fig. 24) triangular with extended keel skewed and pointed on portion toward attachment with hypandrium, in ventral view The lectotype male of Hydrochasma zernyi Hendel, here designated to preserve stability and make more universal the use of this name, is labeled "Unt. Amazonas [Brazil. Pará] 28 Mar-8-15 Sep 1989, 1991 (Cuba, Dominica, Dominican Republic, Grenada, Jamaica, Puerto Rico, St. Lucia, St. Vincent).
Natural History.-This species occurs along freshwater streams and rivers or sometimes brackish water systems (where a freshwater stream or river is entering the ocean) that have sandy areas that are mostly bare of vegetation.

Remarks.
We follow Wirth (1968) in recognizing the two junior synonyms of H. faciale, as noted in the synonymy.
Although this species is externally similar to H. williamsae, as are structures of the male terminalia, they are distinguished from each other in details of the latter structures. The epandrium of this species, for example, is broadly rounded dorsolaterally, not angulate as in H. williamsae, and the ventral margin in lateral view is robustly developed and broadly but unevenly rounded apically, not tapered and pointed as in H. williamsae. Diagnosis. This species is distinguished from congeners by the following combination of characters: Small to moderately small shore flies, body length 1.85-2.60 mm. Head: Subglobose, very broad ventrally, oral opening comparatively large. Pedicel mostly black; medial surface of basal flagellomere extensively yellow, lateral surface with some blackish coloration. Parafacial silvery white, concolorous with face; gena-to-eye ratio 0.32-0.35. Thorax: Mesonotum generally gray but with faint bluish or slightly greenish metallic coloration, especially on posterior portion, including scutellum, not on notopleuron or lateral margins of scutellum; pleural area gray. Wing with costal vein ratio 0.50-0.62; M vein ratio 0.49-0.51. Femora and tibiae gray, tarsi yellow; forefemur lacking a distinctive, comb-like row of stout setulae along anteroventral surface but with a posteroventral row of 5-7 short, spine-like setae; hindtibia bearing a long, spur-like seta ventroapically. Abdomen: Tergites generally dull gray, becoming brownish gray medially; lacking wedge-shaped, gray to silvery gray areas; tergite 5 gray. Male terminalia : Combined structures generally moderately elongate, in posterior view height slightly less than 3× width, generally sparsely setulose, especially dorsally; epandrium with dorsal arch above cerci relatively well developed, thin, completely connected, in posterior view (Fig. 26) as an inverted U on dorsal third to half, ventral portion with lateral margins shallowly concave medially, cruciate subapically, deeply bifurcate medially, medial bifurcation almost as wide as ventral process of epandrium at same level, extended epandrial process tapered, apex rounded; cerci moderately long, height nearly twice width, widely semi-hemispherical ( Fig. 26), not attached lateroventrally with epandrium; aedeagus in lateral view ( Fig. 29) elongate, about 5× longer than wide, tubular, shallowly curved, slightly tapered toward apex with apical portion moderately pointed and with a subapical, rounded projection, in ventral view ( Remarks. The identity of this species has been confused, resulting in misidentifications in collections that we have examined. Structures of the male terminalia of this species are distinctive, however, and distinguish it from congeners, especially the elongated and slender general conformation of these structures, which can only be mistaken with those of H. viridum. Both of these species have elongated, very slender, ventrolateral epandrial processes that are very similar. The hypandrium, especially in ventral view, however, has more elongated, posterolaterally directed processes in H. patens. Additionally, the dorsum of the head and the mesonotum are mostly gray with only faint bluish or greenish coloration.

Remarks.
Structures of the male terminalia of this species are similar to those of H. digitatum but are distinguished from that species in having more robustly developed ventral epandrial processes that are moderately angulate laterally in posterior view. Moreover, the hypandrium of this species in ventral view is much more robustly developed with a broad, bluntly rounded anterior margin. Etymology. The species epithet, sinuatum, is of Latin derivation and means winding or bent, referring to the shape of the extended epandrium in lateral view.
Remarks. Although structures of the male terminalia of this species are similar to those of H. digitatum, they consistently differ in detail. This is particularly evident in the shape of the ventral, epandrial processes where in lateral view there is a basal, posterior notch, and the processes themselves are sinuous and not shallowly arched, as in H. digitatum. The sinuous profile of the ventral, epandrial process is the basis for the name of this species. Diagnosis. This species is distinguished from congeners by the following combination of characters: Small to moderately small shore flies, body length 1.50-2.30 mm. Head: Antenna mostly dark gray; parafacial silvery white, concolorous with facial coloration; gena comparatively high, gena-to-eye ratio 0.47-0.50. Thorax: Wing with costal vein ratio 0.73-1.76; M vein ratio 0.42-0.46. Abdomen: Tergites lacking with broad, shallow, wedge-like marking laterally, otherwise tergites 2-4 with wide medial area extensively dark slate gray (Fig. 71); tergite 5 of male light gray to silvery gray anterior margin and thin, medial stripe brownish gray. Male terminalia (Figs 44-47): Combined structures moderately elongate, in posterior view height about twice width; epandrium with dorsal arch above cerci attenuate, not connected, dorsal ⅔ somewhat angulate laterally, gradually expanded to just ventrad of midheight, thereafter narrowed on ventral third, parallel sided, broadly rounded apically, rounded margin of apex with numerous, medially oriented, relatively robust setulae (Fig. 44), other epandrial setulae oriented medially, in lateral view very narrow dorsally (Fig. 45), lateral of cerci, thereafter ventrally nearly straight with slight, anterior angulate expansion at midheight, narrowly rounded apically; cerci short, in lateral view height about twice width (

Remarks.
As implied by its species' name, spinosum, this species is distinguished from congeners by the numerous spine-like structures on the U-shaped, ventroapical portion of the epandrial process. The angulate, lateral epandrial margins are also distinctive.
Remarks. Externally, the dorsum of the head and mesonotum of this species is unique among congeners, especially species in the faciale group, in having a pronounced, subshiny to shiny, with mostly greenish to bluish luster. Internally, this species could only be confused with H. patens, and indeed, structures of the male terminalia of these two species are similar, although differing in details (compare  with Figs 52-55).
Etymology. The specific epithet, williamsae, is a genitive patronym to honor our colleague and cherished friend, the late Ms Hollis Barton Williams, who provided technical support to us for nearly 35 years. Holly passed away August 23, 2009.
Remarks. This species, as noted previously in the "Remarks" section of H. faciale, is distinguished by structures of the male terminalia, especially the generally short and robust epandrium in posterior and lateral views. The more angulate dorsolateral shoulders (best seen in posterior view) and the tapered and pointed ventral epandrial process are unique to this species and distinguish it from congeners. Width of lateral projections of ventral epandrial extensions greater than length (Fig. 101)  Ventral epandrial extensions parallel sided throughout length with rounded apex (Fig. 111) Lateral margins of epandrium in posterior view distinctly angulate at midheight, then parallel sided, then tapered to apex (Fig. 106) 14 14 Ventral epandrial extensions in lateral view pointed apically (Fig. 97)  apical ½-⅔ abruptly narrowed, parallel sided, apical process not wider than apical ½, apex with very narrow apicomedial cleft, in lateral view (Fig. 66) very elongate, narrow with basal ¾ straight, apical ⅓ becoming slightly wider, slightly expanded, apex narrowly rounded, with paired subapical tooth-like structures on each process; aedeagus in lateral view ( Fig. 68) very elongate and very narrow, mostly parallel sided, apical ⅛ expanded anteriorly and to a less degree posteriorly, apex irregularly rounded, in ventral view (Fig. 67) very narrow and elongate, apical ⅛ bulbously expanded, apex broadly V-shaped; phallapodeme in lateral view (Fig. 68) very narrow and elongate, rod-like, hypandrial end with narrowly pointed keel, aedeagal end very shallowly curved, in ventral view (Fig. 67) elongate, narrow, truncate, slightly and gradually expanded at aedeagal end, hypandrial end with 2 narrow crossbars; gonite in lateral view (Fig. 68) as a very shallowly curved, rod-like process, about equal in length to phallapodeme, in ventral view (Fig. 67) shallowly curved to straight, tapered at both apices; hypandrium in lateral view (Fig. 68)   Etymology. The species epithet, denticum, is of Latin derivation and means tooth, referring to the tooth-like subapical structures toward the apex of the extended epandrium.

Remarks.
As implied by its species' name, denticum, this species is distinguished from congeners by the paired, tooth-like structures located subapically on each of the ventral epandrial processes. In addition, the hypandrium in ventral view is V-shaped with robust, posterior arms that in turn are bifurcate apically.

12.
Hydrochasma distinctum sp. n. http://zoobank.org/4A1D6F9C-A2C5-456A-9EE9-74BF61C84718 http://species-id.net/wiki/Hydrochasma_distinctum Figs 72-76 Diagnosis. This species is distinguished from congeners by the following combination of characters: Moderately small shore flies, body length 2.20 mm. Head: Antenna mostly dark gray; parafacial silvery white, concolorous with facial coloration; gena-to-eye ratio 0.13. Thorax: Wing with costal vein ratio 0.82; M vein ratio 0.51. Forefemur lacking a distinctive, comb-like row of stout setulae along anteroventral surface; tibiae mostly gray. Abdomen: Tergites 3 and 4 with wedge-shaped silverygray areas; otherwise, tergites dark brown to black. Male terminalia (Figs 72-75): Combined structures generally moderately compact and wide, in posterior view height 1.8× width, generally moderately setulose dorsally, setulae sparse or lacking ventrally; epandrium lacking dorsal arch above cerci, in posterior view ( Fig. 72) with basal ⅔ rectangular, lateral margins of basal portion shallowly sinuous, ventral epandrial process conspicuously narrowed, tapered, each process digitiform, bifurcate apically with inverted V-shaped gap between, in lateral view (Fig. 73) much higher than wide, posterior margin arched, anterior margin with a midlength, shallow but elongate concavity, apex obtusely rounded; each ventral epandrial process with 2-3 dentate structures subapically; aedeagus in lateral view (Fig. 75) basically elongate, slender, tubular, tapered toward apex but with a large, somewhat quadrate structure at midlength, in ventral view ( Fig. 74) elongate, slender, tubular, with quadrate structure at midlength, quadrate structure with basal margin shallow emarginate, apical margin with wide, shallow projection, truncate apically; phallapodeme in lateral view ( Fig. 75) elongate, narrow, shallowly sinuous, keel as irregular, apical knob, in ventral view (Fig. 74) elongate, narrow, T-shaped, truncate at each end, basal half gradually expanded; gonite in lateral view (Fig. 75) a very shallowly sinuous, rod-like process, about ¾ length of phallapodeme, in ventral view (Fig. 74) shallowly sinuous, bluntly rounded at both apices; hypandrium in lateral view (Fig. 75) narrowly developed, generally narrowly ovate, anterior margin moderately narrowly rounded, gradually tapered toward posterior margin, in ventral view (Fig. 74)  Remarks. Thus far, this species is known only by the holotype male. As implied by its species' name, distinctum, this species is readily distinguished from congeners by the distinctive structures of the male terminalia, which are unique among congeners. The shape of the epandrium with a somewhat large and rectangular base and the short, tapered, ventral epandrial processes that bear tooth-like structures subapically are unique, as is the aedeagus that has a relatively large, quadrate structure at its midlength. Only H. denticum, which also has subapical tooth-like structures on the ventral epandrial processes, is similar. The ventral epandrial processes of H. denticum, however, are much longer than their base, the aedeagus does not have a quadrate structure at its midlength, and the hypandrium is V-shaped. Diagnosis. This species is distinguished from congeners by the following combination of characters: Small shore flies, body length 1.65-1.90 mm. Head: Antenna mostly dark gray; parafacial silvery white, concolorous with facial coloration; gena-to-eye ratio 0.21-0.23. Thorax: Wing with costal vein ratio 0.69-0.71; M vein ratio 0.49-0.52. Forecoxa yellowish to tan; forefemur lacking a distinctive, comb-like row of stout setulae along anteroventral surface; tibiae mostly gray. Abdomen: Tergites 3-4 with distinct, deep, wedge-like marking laterally but tergites 2-4 with wide medial area extensively dark slate gray to black; tergite 5 light gray to silvery gray with undifferentiated posterior margin, uniformly colored (Fig. 142); medial coloration on tergites 1-4 narrow, sometimes only a stripe, slightly darker than color of lateral margins. Male terminalia (Figs 77-80): Combined structures generally elongate, in posterior view height nearly 2.5× width; epandrium ( Fig. 77) with dorsal arch above cerci attenuate, not connected, dorsal ⅓-½ somewhat quadrate with angles rounded, ventral portion as 2 digitiform, thick, abutting, parallel lobes that connect subapically for a short distance, ventral margin concave with a medial, narrow incision, dorsal half bearing longer setulae than ventrally, ventral setulae lacking on apical portion, in lateral view (Fig. 78) mostly parallel sided and nearly straight, apical ⅛ angled anteroventrally as a tapered, narrowly pointed apex; cerci relatively very short, in lateral view (Fig. 77) height about twice width, narrowly semicircular, attached to epandrium ventrally; aedeagus in lateral view (Fig. 80) elongate, with length of sclerotized portion about 8× width, basal portion parallel sided, apical half greatly enlarged, bulbous, membranous, with apex broad, membrane bearing sub-basally numerous scale-like spicules, in ventral view (Fig. 79) also showing expanded apex, basal ½ comparatively narrowed, slightly wider at base, thereafter slightly tapered to expanded, broadly obovate apical half; phallapodeme in lateral view (Fig. 80) narrow, very elongate, evenly shallowly arched, keel very weakly developed, barely evident at end toward attachment with hypandrium, in ventral view ( Fig. 79) with hypandrial end T-shaped with 2 crossbars, thereafter toward base of aedeagus gradually expanded to blunt apex; gonite in lateral view (Fig. 80) narrow, elongate, bar-like with slight, sinuous curvature, in ventral view (Fig. 79) moderately narrow, elongate, rod-like, apices narrowed; hypandrium in lateral view (Fig. 80) elongate, roughly rectangular, moderately shallow, width slightly more than ¼ length, very slightly angulate, in ventral view (Fig. 79) generally U-shaped with base very thick, posterior margin deeply U-shaped, anterior margin moderately narrowly rounded. Etymology. The species epithet, dolabrutum, is of Latin derivation and means axe, referring to the shape of the extended epandrium in lateral view.
Remarks. Structures of the male terminalia of this species are similar to those of H. parallelum but are distinguished from the latter species by having a comparatively more robust extended epandrial process (best seen in posterior view). Moreover, the hypandrium in general is wider, more robustly developed, and the anterior margin is broadly rounded rather than truncate as in H. parallelum. gray; hindtibia bearing an ventroapical, spur-like seta. Abdomen: Tergites 3-4 with distinctive, deep, gray wedge-like marking along lateral margin of darkened, dorsal coloration; tergite 5 of male gray with posteromedial area darkened. Male terminalia (Figs 81-84): Epandrium generally elongate, setulae moderately sparse, on medial portion, in posterior view (Fig. 81) with dorsal arch attenuate, not connected, dorsal ⅔-¾ somewhat diamond shaped, widest just ventrad of cerci, thereafter ventrally tapered to arrow-shaped apex, arrow-shaped apex with width subequal to length, apex with narrowly incised medially, in lateral view (Fig. 82) narrowly elongate, mostly parallel sided, anterior margin shallowly sinuous, apex somewhat bluntly rounded; cerci short, length in lateral view (Fig. 82) slightly more than twice width, hemispherical; aedeagus in lateral view (Fig. 84) relatively simple, narrowly tubular, length 5× width, in ventral view (Fig. 83) also tubular, narrow, elongate; phallapodeme in lateral view (Fig. 84) linear, very shallowly curved, extended keel narrow and short, as a slight bump, in ventral view (Fig. 83) narrowly Y-shaped with apical arms short and with short, subapical crossbar; gonite in lateral view (Fig. 84) narrowly elongate, bar-like, more curved than phallapodeme, in ventral view (Fig. 83) narrowly bar-like, elongate, nearly straight; hypandrium in lateral view (Fig. 84) elongate, length about ⅔ that of aedeagus, straight, rod-like, slightly expanded on apical half, in ventral view (Fig. 83) with anterior margin broadly truncate, lateral margins nearly parallel sided, posterior margin deeply incised with bifurcate, short, processes sublaterally.

Hydrochasma falcatum
Type material. The holotype male of Hydrochasma falcatum is labeled "PERU. Etymology. The species epithet, falcatum, is of Latin derivation and means sickle shaped, referring to the sickle-shaped gonite in lateral view.
Remarks. Like H. glochium and to a lesser degree like H. urnulum, this species has an expanded apical portion of the extended epandrial process (best seen in posterior view). That process, however, has only moderate, lateral extensions (Fig. 81). The hypandrium of H. falcatum is somewhat rectangular in ventral view with a distinct, V-shaped posteromedial emargination (Fig. 83). In males of H. glochium, the expanded apical portion is more pronounced (Fig. 86), and the hypandrium in robustly Vshaped (Fig. 88). This species is also like those of the faciale group in having a spur-like seta ventroapically on the hindtibiae. Diagnosis. This species is distinguished from congeners by the following combination of characters: Small shore flies, body length 1.65-1.95 mm. Head: Antenna mostly dark gray; parafacial silvery white, concolorous with facial coloration; gena-to-eye ratio 0. 19-0.21. Thorax: Wing with costal vein ratio 0.72-0.74; M vein ratio 0.50-0.53. Forecoxa whitish gray basally, apical ⅔-¾ yellow; forefemur lacking a distinctive, comb-like row of stout setulae along anteroventral surface; tibiae mostly yellow; hindtibia with silvery gray, broad band medially. Abdomen: Tergites 3-4 with deep, silvery gray wedges laterally; tergite 5 mostly silvery gray, only anterior brownish black, and with faint blackish coloration posteriorly. Male terminalia (Figs 86-89): Combined structures generally moderately elongate, in posterior view height slightly less than 3× width, generally sparsely setulose, more so dorsally, setulae sparse medially, setulae becoming smaller ventrally; epandrium lacking dorsal arch above cerci, in posterior view ( Fig. 86) with apical ½ abruptly narrowed, mostly parallel sided, apical process conspicuously wider than apical ½, flared laterally subapically, apex with very narrow apicomedial V-shaped cleft, in lateral view (Fig. 87) elongate, narrow, generally shallowly curved, apical process with subapical expansion, apex bluntly rounded; aedeagus in lateral view (Fig. 89) very elongate and narrow, generally expanding toward apex, apical ½ with tiny, cuticular, narrow projections, apical ¼ with complex folding, apex skewed anteriorly, narrowly pointed, in ventral view (Fig. 88) generally narrow and elongate, slightly narrowed at midlength, apical ⅓ slightly expanded, moderately bulbous, apex broad; phallapodeme in lateral view (Fig. 89) very narrow and elongate, rod-like to narrowly clavate, gradually expanded from aedeagal end to hypandrial end, latter with very narrowly pointed keel, aedeagal end straight, in ventral view (Fig. 88) elongate, narrow, truncate at both ends, slightly and gradually expanded at aedeagal end, hypandrial end with 2 narrow crossbars; gonite in lateral view (Fig. 89) as nearly straight, rod-like process, almost equal in length to phallapodeme, in ventral view (Fig.  88) nearly straight, very slightly wider medially, tapered at both apices; hypandrium in lateral view (Fig. 89) narrowly developed, posterior half narrowly angled, tapered toward anterior margin, narrowly angulate anteriorly, in ventral view (Fig. 88) moderately deeply and narrowly V-shaped, arms of V generally thick, pointed posteriorly, anteromedially margin bluntly rounded.  Etymology. The species epithet, glochium, is of Greek derivation and means arrow head, referring to the arrow-like apex of the ventral extension of the epandrium.
Remarks. In the remarks section of the previous species (p. 61), we noted characters to distinguish this species from H. falcatum, particularly the more pronounced, lateral extensions of the apical portion of the ventral, the epandrial process, and the robust, V-shaped, hypandrium. (Figs 86-88). ( Hendel, 1930: 138. Cresson 1938.

Hydrochasma incisum
Diagnosis. This species is distinguished from congeners by the following combination of characters: Small to moderately small shore flies, body length 1.35-2.05 mm. Head: Antenna mostly dark gray; parafacial silvery white, concolorous with facial coloration; gena-to-eye ratio 0.18-0.20. Thorax: Wing with costal vein ratio 0.56-0.58; M vein ratio 0.50-0.51. Forecoxa with base silvery white to gray, apical ⅔ yellowish; forefemur lacking a distinctive, comb-like row of stout setulae along anteroventral surface; tibiae mostly gray. Abdomen: Tergites 3-4 with distinctive, deep, wedge-like lateral margin of darkened dorsum; tergite 5 of male mostly gray with posterior margin blackish. Male terminalia (Figs 91-94): Combined structures generally elongate, in posterior view height less than 3× width (2.8×), generally sparsely setulose, especially dorsally, setulae sparse medially along dorsal ⅔; epandrium lacking dorsal arch above cerci, in posterior view (Fig. 91) with apical ½ abruptly narrowed, mostly parallel sided, apical process wider than apical ½ and angled ventrolaterally, apex with very narrow apicomedial cleft, in lateral view (Fig. 92) very elongate, narrow with basal ¾ straight, apical ½ narrow to just before slightly broadened and curved apex, apex narrowly rounded; aedeagus in lateral view (Fig. 94) very elongate and narrow, shallowly sinuous, mostly parallel sided, apical ¼ [or ⅓] with complex folding and secondary structures, apex rounded, in ventral view (Fig. 93) very narrow and elongate, apical ¼ [or ⅓] very bulbously expanded, apex broad; phallapodeme in lateral view (Fig. 94) very narrow and elongate, rod-like, hypandrial end with very narrowly pointed keel, aedeagal end straight, in ventral view (Fig. 93) elongate, narrow, truncate at both ends, slightly and gradually expanded at aedeagal end, hypandrial end with 2 narrow crossbars; gonite in lateral view (Fig. 94) as a very shallowly sinuous, rod-like process, about equal in length to phallapodeme, in ventral view (Fig. 93) (6642) [red]. The lectotype is double mounted (glued to a paper triangle), is in good condition (structures of male terminalia exposed), and is deposited in the USNM (6642)." Coquillett (1902: 183) noted that the type series comprised eight specimens with no single specimen designated as the type or holotype. Two of the eight specimens are missing (pins with labels still extant, specimens missing). From the other six specimens (Vieques Island, Fajaro, Mayaquez, Aguadillo, Utuado and Arroyo), we selected the male from Mayaquez list above as the lectotype because it is in good condition and is easily identified to species. The other specimens, here designated as paralectotypes, appear to be conspecific (we did not make dissections of the other males), but one paralectotype from Vieques Island appears to be a male of H. leucoproctum.
The  Remarks. This is a widespread and common species in much of the Neotropics. We have relied primarily on structures of the male terminalia to accurately identify this species, especially the elongated, slender, ventral epandrial process, which distinguishes this species. This structure is often partially or wholly exposed, allowing for identification in dried, pinned males.
We have observed slight variation in some specimens, usually whether the aedeagal apex is slightly inflated or not, but also in the length of the ventral epandrial process. We interpret this variation to be intraspecific, which may be an artifact in part of how specimens were preserved. Diagnosis. This species is distinguished from other congeners by the following combination of characters: Small shore flies, body length 1.25-1.80 mm. Head: Antenna mostly dark gray; parafacial silvery white, concolorous with facial coloration; genato-eye ratio 0.17-0.18. Thorax: Wing with costal vein ratio 0.65-0.67; M vein ratio 0.54-0.58. Forecoxa mostly gray to silvery gray, some yellowish coloration at ventral apex; forefemur lacking row of spine-like setulae along anteroventral surface; tibiae mostly gray; hindtibia lacking a long, spur-like seta ventroapically. Abdomen: Tergites 3-4 with moderately deep, gray to silvery gray wedges at lateral margins; tergite 5 of male mostly to entirely gray, sometimes with posterior margin darkened. Male terminalia (Figs 96-99): Epandrium generally elongate, almost 3 times longer than wide, and setulose, in posterior view ( Fig. 96) with dorsal arch attenuate, not connected, dorsal ⅓ somewhat rectangular, ventral ⅔ tapered with lateral margins shallowly sinuous to a pointed ventral margin, ventromedial apex incised, narrowly V-shaped, in lateral view (Fig. 97) very narrowly developed dorsally laterad of cerci, thereafter ventrally becoming slightly wider to midlength, then becoming wider at ventral ⅓, before becoming tapered to pointed ventral margin; cerci short, length less than twice width, in posterior view (Fig. 96) hemispherical with pointed dorsal apex and truncate ventral margin, in lateral view (Fig. 97) almost evenly semicircular; aedeagus in lateral view (Fig. 99) relatively simple, narrowly tubular except for expanded, mostly membranous apex, length 6-7× width, in ventral view (Fig. 98) tubular; phallapodeme in lateral view (Fig. 99) spatulate with width of keel equal to width of phallapodeme, keel or spatulate end at end toward hypandrium, rest of phallapodeme tapered, curved subapically toward aedeagus, in ventral view (Fig. 98) linear, with slightly and narrowly developed T-shaped extensions; gonite in lateral view (Fig. 99) bar-like, narrowly linear, sinuous, in ventral view (Fig. 98) short, somewhat shallowly zig-zag; hypandrium in lateral view (Fig. 99)   Etymology. The species epithet, kaieteur, is the name of the world-famous falls in Guyana where this species was collected. The name is a noun in apposition.

Hydrochasma miguelito
Etymology. The species epithet, miguelito, is to recognize Michael W. Mathis who is also known as "Don Miguel" or "Miguelito." Michael guided us while conducting field work in Honduras where this species was collected. We are treating miguelito as a noun in apposition.
Remarks. Structures of the male terminalia readily distinguish this species from congeners, especially those of the incisum group. Certainly unique to this species is the greatly expanded apical portion of the ventral, epandrial process, which is like a broad arrowhead. The expanded, ventral, epandrial process can be seen in ventral and somewhat in lateral views. The rectangular hypandrium that has a moderately deep and wide posterior emargination is also characteristic. ventral portion with each lateral half robustly developed, parallel sided then apical nearly half tapered to ventral apex, apex pointed, narrowly incised medially along entire length from cercal cavity to apex, in lateral view (Fig. 107) very shallow L-shaped, obtuse angle, ventral ⅓ tapered to narrowly rounded apex; cerci moderately short, height more than twice width, widely semi-hemispherical ( Fig. 106), pointed dorsally, not attached lateroventrally or ventrally with epandrium; aedeagus in lateral view (Fig. 109) very elongate, almost 6× longer than width, tubular, shallowly curved, apex rounded and with a subapical rectangular extension, in ventral view (Fig. 108) mostly tapered from base apical, rounded expansion; phallapodeme in lateral view (Fig. 109) narrowly elongate with extended keel small, short and barely extended, skewed, irregularly rectangular on portion toward attachment with hypandrium, in ventral view (Fig. 108) an elongate, moderately narrow Y with arms of Y very short; gonite in lateral view (Fig. 109) narrow, elongate, bar-like, very shallowly and obtusely angulate, in ventral view (Fig. 108) shallowly angulate; hypandrium in lateral view (Fig. 109) moderately elongate, very shallow, tapered to curved point anteriorly, in ventral view (Fig. 108) Zatwarnicki, USNM [red]." The holotype is double mounted (glued to a paper triangle)), is in excellent condition, and is deposited in the USNM. Eight paratypes (6♂, 2♀; USNM) bear the same label data as the holotype. Other paratypes are as follows: ECUADOR. Guayas: Río Bobo (01°53.8'S, 79°42'W), Aug 1955, R. Levi-Castillo (3♂, 1♀; USNM).
Remarks. Externally, this species is very similar to H. incisum and has often been misidentified as that species in collections. Structures of the male terminalia are quite different, however, and readily distinguish between these two species. In addition, the apex of the wing in H. octogonum is acutely angulate, and the vertex of the angle, the apex, is faintly to conspicuously infuscate. In specimens of H. incisum, the apex is narrowly rounded and hyaline, typical of most congeners.
Distribution (Fig. 105). Neotropical: Trinidad and Tobago. Etymology. The species epithet, parallelum, is of Latin derivation and means parallel sided, referring to the parallel sided extensions of the epandrium.
Remarks. Structures of the male terminalia of this species are similar to those of H. dolabrutum but are distinguished from the latter species by having a comparatively more slender extended epandrial process (best seen in posterior view). Moreover, the hypandrium in general is thinner, more slenderly developed, and the anterior margin is truncate rather than being broadly rounded as in H. dolabrutum. Diagnosis. This species is distinguished from other congeners by the following combination of characters: Small shore flies, body length 1.40-1.90 mm. Head: Antenna mostly dark gray; parafacial silvery white, concolorous with facial coloration; gena-toeye ratio 0. 16-0.18. Thorax: Wing with costal vein ratio 0.73-0.74; M vein ratio 0.51-0.53. Forecoxa usually mostly yellow (apical ½-⅔); tergites 3-4 with lateral wedges, sometimes deeply inset. Abdomen: Tergites 3-4 with moderate deep gray wedges at lateral margin of darkened dorsum, wedge of tergite 4 deeper; tergite 5 of male mostly gray, with posterior margin darkened. Male terminalia (Figs 115-118): Combined structures generally moderately elongate, in posterior view height almost 2.5× width, generally setulose dorsally, setulae sparse or lacking ventrally; epandrium lacking a dorsal arch above cerci, in posterior view (Fig. 115) with apical ⅓-½ abruptly narrowed, mostly parallel sided, phallic-like with apex expanded, hood-like, apicomedially with narrow, short cleft, in lateral view (Fig. 116) generally very shallowly arched, elongate, narrow, wider basally; cerci moderately short, height nearly twice width, semi- Distribution (Fig. 119). Neotropical: Brazil (Amazonas), Trinidad and Tobago, West Indies (Antigua, Cuba, Dominican Republic, Grenada, Jamaica, Puerto Rico).

Hydrochasma peniculum
Etymology. The species epithet, peniculum, is of Latin derivation and means tail or penis, referring to the shape of the epandrial extensions.
Remarks. This species is similar to H. incisum in having the dorsal half of the epandrium somewhat rectangular and in lacking a dorsal connecting band above the cerci, and the ventral portion, the ventral, epandrial process, is distinctly narrower in both species. This species is distinguished from H. incisum, however, in having a parallel-sided ventral epandrial process that is not as long but is more robustly developed than in H. incisum, and the apical portion is more expanded.
Remarks. Among congeners, especially those of the incisum group, this species is distinguished by its simplicity, hence its species name. The epandrium, including the ventral epandrial processes, are simple, mostly straight and unadorned, as is the aedeagus, gonite, and hypandrium (Figs 120-123).
Etymology. The species epithet, urnulum, is of Latin derivation and means urn, referring to the urn-shaped hypandrium in ventral view.
Remarks. Like H. glochium, H. urnulum has an expanded apical portion of the extended epandrial process but only slightly so (best seen in posterior view). The hypandrium of H. urnulum is deeply and thinly V-shaped in ventral view with a distinct, Ushaped, posteromedial emargination (Fig. 129). In males of H. glochium, the expanded apical portion of the epandrium is more pronounced (Fig. 86), and the hypandrium is V-shaped (Fig. 88)  Diagnosis. This species group is distinguished from others within Hydrochasma by the following combination of characters: Head: Oral opening small, not gaping. Thorax: Hindtibia lacking a prominent, spur-like, ventral, subapical seta. Abdomen: Tergites with a sharply demarcated, straight lateral line, lacking lateral wedges. Male terminalia: Ventral epandrial extensions usually somewhat narrow and parallel-sided, at least at base; ventral margin of epandrium variable, if bifurcate, gap narrow and relatively shallow.

Key to species of the leucoproctum group
1 Forecoxa mostly to entirely yellowish; face mostly creamy yellow distinctly contrasting in coloration with white to silvery white parafacial, lateral margin of face, immediately adjacent to parafacial dark brown (except H. sagittarium which has a non-contrasting facial color Parafacial and face essentially the same color, not distinctly contrasted; ventral extensions of epandrium with apical ⅓ arrow-like in posterior view (Fig. 191)
Etymology. The species epithet, annae, is a feminine genitive patronym to recognize Ms. AnnaLee Thayn who inspired us while collecting in the Southwest.
Remarks. Externally, this species is very similar and evidently closely related to H. andeum and H. avanae but can be distinguished from either of these two species by having a hindtibia with only yellowish setulae ventrally near the apex, less sinuous margins of the epandrium, and by having a more delicately developed hypandrium that is deeply V-shaped in ventral view (Fig. 139).
Etymology. The species epithet, aquia, is a noun in apposition and is the name for the general area, including Aquia Creek and Aquia Harbour, where the type series of this species was collected. Aquia is the transliterated name of a Native American village (Powhatan Confederacy) located near mouth of Aquia Creek in present day Stafford County, Virginia. The name, which was originally spelled phonetically as "Quiyough," apparently means gulls, a common bird on the creek.
Remarks. This is a widespread species that is relatively common in the Nearctic Region. Externally, this species is very similar and evidently closely related to H. andeum, H. avanae, and H. annae but can be distinguished from these species by having a hindtibia that bears only yellowish setulae ventrally near the apex, a tapered ventral epandrial process, and by having a more delicately developed hypandrium that is deeply U-shaped in ventral view (Fig. 146). Combined structures generally elongate, in posterior view (Fig. 149) height about 2.5× width; epandrium with dorsal arch above cerci attenuate, not connected, dorsal ⅓-½ somewhat quadrate with angles rounded, ventral portion as 2 digitiform, thick, parallel lobes that connect subapically for a short distance, ventral margin moderately narrowly rounded with deep, very narrow, apical incision medially, dorsal half bearing setulae, in lateral view (Fig. 150) mostly parallel sided with anterior shallowly sinuous, apical ⅓ tapered to sharply rounded apex; cerci short, in lateral view height about twice width (Fig. 150), narrowly semicircular, not attached with epandrium; aedeagus in lateral view (Fig. 152) elongate, with length of sclerotized portion about 5× width, with greatly enlarged apical and ventral, membranous portion, shape in lateral view ( Fig.  152) triangular, with apex broad and shallowly arched, thereafter toward base tapered to narrow, bluntly rounded margin, membrane bearing sub-basally numerous scalelike spicules, in ventral view (Fig. 151) also showing expanded apex, basal ⅓ narrowed, thereafter with middle portion ballooning out to more than twice basal width, apical ⅓ greatly expanded, broadly obovate; phallapodeme in lateral view (Fig. 152) narrow, elongate, evenly shallowly arched, keel weakly developed, barely evident at end toward attachment with hypandrium, in ventral view ( Fig. 151) with hypandrial end narrowly T-shaped, thereafter toward base of aedeagus gradually expanded to blunt apex; gonite in lateral view (Fig. 152) narrow, elongate, bar-like with slightly curvature, in ventral view (Fig. 151) moderately broad but with apices narrowed, especially end toward hypandrium; hypandrium in lateral view ( Fig. 152) elongate, moderately shallow, width slightly more than ¼ length, very slightly angulate, in ventral view (Fig. 151) generally V-shaped with posterior margin deeply U-shaped, anterior margin moderately narrowly rounded.  Diagnosis. This species is distinguished from other congeners by the following combination of characters: Small to moderately small shore flies, body length 1.25-2.15 mm. Head: Antenna mostly dark gray; parafacial silvery white, concolorous with facial coloration; gena-to-eye ratio 0. 16-0.17. Thorax: Wing with costal vein ratio 0.68-0.71; M vein ratio 0.60-0.62. Forecoxa mostly to entirely yellow, at most with basal margin gray to silvery gray. Abdomen: Tergites 1-4 with dorsum extensively grayish black to slate black, sharply contrasted along an even line with gray to silvery gray lateral margins (margins sometimes on venter), lacking gray wedges along lateral margins; tergite 5 of male with gray anterior margin, posterior portion with a large, medial, oval, black spot (Fig. 184). Male terminalia (Figs 157-160): Combined structures generally moderately elongate, in posterior view (Fig. 157) height slightly more than twice width, generally setulose but with setulae on ventral ⅓ smaller than those on dorsal ⅔; epandrium with dorsal arch above cerci roundly truncated, not connected, in posterior view (Fig. 157) with wide medial area membranous, narrowest at midlength, sclerotized ventral portion (along margin) tapered to sharp point, ventral margin very broadly rounded, in lateral view (Fig. 158) (Cuba, Dominican Republic, Jamaica, Puerto Rico, St. Lucia).

Hydrochasma avanae
Etymology. The species epithet, capsum, is of Latin derivation and means case, referring to the rectangular, case-like shape of the male terminalia in posterior view.
Remarks. This species is closely related to H. robustum, especially the similar shapes of their respective epandriums in posterior view, but it can be distinguished from that species by the more broadly developed hypandrium in ventral view (wider than long) and the lack of basal, hypandrial notches. Diagnosis. This species is distinguished from other congeners by the following combination of characters: Small shore flies, body length 1.55-1.75 mm. Head: Antenna mostly dark gray; parafacial silvery white, concolorous with facial coloration; genato-eye ratio 0. 16-0.17. Thorax: Wing with costal vein ratio 0.67-0.69; M vein ratio 0.52-0.54. Forecoxa mostly blackish gray to gray. Abdomen: Tergites 1-4 extensively brownish black to blackish gray dorsally, lacking lateral wedges. Male terminalia (Figs 162-165): Combined structures generally moderately elongate, in posterior view height twice width, excluding cerci, generally setulose dorsally, setulae sparse or lacking ventrally; epandrium with dorsal arch above cerci interrupted, not connected, in posterior view (Fig. 162) with basal half rectangular with angles rounded, apical half narrowed, extended as abutting, narrow, almost parallel sided processes until irregularly rounded apex, rounded apex with broad, shallow triangular extension; ventral extensions of epandrium with subapical, shallowly V-shaped structure that bears setulae, in lateral view (Fig. 163) generally moderately deeply arched with curvature more evident medially, apex rounded; cerci moderately short, height nearly twice width, semi-hemispherical (Fig. 162), attached ventrally with epandrium; aedeagus in lateral view (Fig.  165) elongate, about 4× longer than subapical width, tubular on basal half, mostly parallel sided, expanded on apical half, in ventral view (Fig. 164) almost diamond shaped with longer basal extension being parallel sided, apex rounded; phallapodeme in lateral view (Fig. 165) narrowly elongate, moderately expanded toward anterior margin, keel as a narrow, digitiform process, in ventral view (Fig. 164) an elongate T with arms moderately wide, extended vertical shaft expanded to aedeagal base, this end truncate; gonite in lateral view (Fig. 165) narrowly elongate, bar-like, very shallowly V-shaped, in ventral view (Fig. 164) narrowly elongate, slightly swollen medially; hypandrium in lateral view (Fig. 165)  base, posterior margin tapered to a slightly recurved point, anterior margin truncate, in ventral view (Fig. 164)

Remarks.
Although similar to congeners of the leucoproctum group, this species is readily distinguished from them by the shape of the epandrium, especially the ventral epandrial process that is parallel-sided and has a uniquely shaped apical one-fourth. Subapically, the ventral epandrial process bears a broad and shallowly V-shaped row of tiny setulae. The hypandrium is V-shaped with a moderately well-developed anterior base and a U-shaped, posteromedial, hypandrial emargination. The posterior hypandrial arms are slightly divergent and delicately developed.  167) with dorsal half somewhat quadrate, bearing some setulae medially, shallowly pedunculate near mid length, ventral portion generally lacking setulae, as 2, nearly parallel-sided, elongate processes, ventral margin V shaped, deeply incised medially, in lateral view (Fig. 168) as an elongate, shallowly curved structure, widest subapically, apex pointed; cerci short, height not quite twice width (Fig. 167), not attached lateroventrally with epandrium; aedeagus in lateral view (Fig. 170) elongate, over 5× longer than width, basal ¾ tubular, thinly cigar-shaped, apical ¼ membranous, expanded, in ventral view (Fig. 169) essentially parallel sided, apex pointed; phallapodeme in lateral view (Fig. 170) narrow, elongate, unevenly spatulate with widened keel end toward hypandrium, opposite end slightly tapered and curved, keel short and narrow, in ventral view (Fig. 169) narrowly T-shaped with arms short and right angled; gonite in lateral view (Fig. 170) narrow, elongate, bar-like, shallowly curved, in ventral view (Fig. 169)   Etymology. The species epithet, garvinorum, is a pleural Latin genitive patronym to honor John Robert and Melodee Garvin (née Bodell), who guided us to the type locality on the Hazel River, which is located in the foothills of the Blue Ridge during the summer of 2008.

Hydrochasma garvinorum
Remarks. This species is similar to H. annae but is distinguished from it by the more robustly developed ventral epandrial process in posterior and lateral views , and the rectangular shaped hypandrium that has a moderately deep, posteromedial hypandrial emargination. ( Fig. 176) with ventral ⅔ narrow, almost parallel sided with subapical, slightly narrowing, apical portion oriented anteriorly slightly, apex rounded; cerci short, height not quite twice width (Fig. 175), tenuously attached lateroventrally with epandrium; aedeagus in lateral view (Fig. 178) elongate, over 5× longer than width, tubular, slightly arched, with apical portion somewhat rectangular, in ventral view (Fig. 177) essentially parallel sided, apex pointed; phallapodeme in lateral view (Fig. 178)  Remarks. This is one of the more common species of the genus in eastern North America and is found from Michigan and Pennsylvania south into northern South America. In the Delmarva States, this is likewise a widespread species, occurring along the coastal plain, Piedmont, Blue Ridge, and Alleghany zones.

Hydrochasma leucoproctum
This species is distinguished from others of the leucoproctum group by the uniquely shaped epandrium, especially the ventral epandrial process, which is generally tapered until the apical portion that is parallel sided. In addition the hypandrium is H-shaped, having both anterior and posterior emarginations. Diagnosis. This species is distinguished from other congeners by the following combination of characters: Small shore flies, body length 1.20-1.70 mm. Head: Antenna mostly dark gray; parafacial silvery white, concolorous with facial coloration; gena-to-eye ratio 0.18-0.19. Thorax: Wing with costal vein ratio 0.70-0.72; M vein ratio 0.53-0.56. Forecoxa mostly blackish gray to gray. Abdomen: Tergites 1-4 extensively brownish black to blackish gray dorsally, lacking lateral wedges. Male terminalia (Fig. 180-183): Combined structures generally elongate, in posterior view height nearly 4× width, generally sparsely setulose, setulae especially sparse over midsection; epandrium with dorsal arch above cerci interrupted, not connected, in posterior view ( Fig. 180) with basal third rectangular with angles rounded, apical ⅔ narrowed, linear, extended as abutting, narrow, almost parallel sided processes, apex tapered to a point, in lateral view (Fig. 181) generally elongate and narrow, ventral ⅔ essentially parallel sided, linear, apex rounded; cerci moderately short, height nearly twice width, semi-hemispherical (Fig. 180), fused ventrally to epandrium; aedeagus in lateral view (Fig. 183) generally very elongate and narrow, narrowly tubular, length over 10× width, mostly parallel sided, in ventral view (Fig. 182) elongate, narrow, tubular, parallel sided, apex rounded; phallapodeme in lateral view (Fig. 183) narrowly elongate, moderately and conspicuously expanded toward anterior margin, keel as a irregularly tapered extension, in ventral view (Fig. 182) clavate with gradually widened basal portion and anterior apex narrowly T-shaped; gonite in lateral view (Fig. 183) narrowly elongate, bar-like, very shallowly arched, in ventral view (Fig. 182) narrowly elongate, very shallowly sinuous; hypandrium in lateral view (Fig. 183) elongate, very shallow, nearly flat and parallel sided, in ventral view (Fig. 182) moderately deeply V-shaped, with anterior portion moderately robustly developed, tapered toward anterior, rounded apex, posterior margin deeply V-shaped.
Type material. The holotype male of Hydrochasma lineatum is labeled "TRIN-IDAD. St Distribution (Fig. 100). Neotropical: Trinidad and Tobago (Tobago, Trinidad). Etymology. The species epithet, lineatum, is of Latin derivation and mean linear, referring to the straight, line-like shape of the epandrium in posterior and lateral views.
Remarks. This species is distinguished from congeners of the leucoproctum group by the very elongated ventral epandrial processes that are mostly parallel-sided, although tapered subapically to the apex. In addition, the hypandrium is uniquely shaped, being elongated, slender, and with an elongated anterior base that is almost twice the length of the depth of the posteromedial, hypandrial emargination.
Etymology. The species epithet, robustum, is of Latin derivation and means robust, referring to the generally robust structures of the male terminalia.
Remarks. This species is very similar and is evidently closely related to H. capsum, as evidenced by the similar shapes of their respective epandriums in posterior view. This species can be distinguished from H. capsum by the more elongated hypandrium in ventral view (longer than wide) and the unique, basal, hypandrial notches (best seen in lateral view; Fig. 189).

Hydrochasma sagittarium sp. n.
http://zoobank.org/435DD268-B483-4536-A11A-1271A4349ABF http://species-id.net/wiki/Hydrochasma_sagittarium  Diagnosis. This species is distinguished from other congeners by the following combination of characters: Small shore flies, body length 1.35-1.75 mm. Head: Antenna mostly dark gray; parafacial silvery white, concolorous with facial coloration; gena comparatively short, gena-to-eye ratio 0.10-0.11. Thorax: Wing with costal vein ratio 0.67-0.70; M vein ratio 0.49-0.52. Forecoxa mostly yellowish orange; tergites 1-4 blackish gray dorsally. Abdomen: Tergites 1-4 broadly slate black on dorsum with sharply demarked gray lateral margin, without wedges, and gray ventral surface, tergite 5 of male gray with slate-black posterior margin. Male terminalia : Epandrium generally elongate and setulose, in posterior view (Fig. 191) with dorsal arch attenuate, not connected, dorsal ⅔-¾ narrowly diamond shaped, widest just ventrad of cerci, thereafter ventrally tapered to arrow-shaped apex, arrow-shaped apex with length twice width, apex with narrowly incised medially, in lateral view (Fig. 192) narrowly elongate, mostly parallel sided, slightly wider at beginning of arrow-shaped apex, apex narrowly rounded; cerci elongate, length about 3× width, medial margin shallowly sinuous (Fig. 191), dorsal apex pointed, oriented medially, narrowly hemispherical, in lateral view (Fig. 192) more robust than posterior view, length slightly more than twice width; aedeagus in lateral view (Fig. 194) relatively simple, narrowly tubular, length 11× width, in ventral view (Fig. 193) also tubular; phallapodeme in lateral view (Fig. 194) linear, conspicuously curved, more so toward hypandrium, ex- both of these species have some characters of the genus Hydrochasma, most notably the high gena. Herein, we revise both of these species, providing descriptions and illustrations of the male terminalia that detail the basis for including both species in the genus Discocerina. Structures of the male terminalia, especially fusion of the phallapodeme with the base of the aedeagus, are the primary basis for this their inclusion in Discocerina.
Type material. Diagnosis. This species is distinguished from congeners by the following combination of characters: Generally densely microtomentose, whitish gray to blackish gray. Moderately small shore flies, body length 2.55 mm. Head: Frons mostly yellow, ocellar triangle gray; area immediately laterad of ocellar triangle brownish yellow; frontoorbits whitish gray; pseudopostocellar setae well developed, length subequal to proclinate fronto-orbital seta. Antenna yellow; arista bearing 5-6 dorsally branching rays. Face mostly faintly yellow, becoming more whitish yellow ventrally and on dorsal portion of antennal grooves; bearing 3 larger setae in vertical row and with a small seta at ventral extent of row. Eye ratio 0.80. Gena high, mostly silvery white, gena-to-eye ratio 0.35. Thorax: Mesonotum mostly faintly grayish tan, becoming grayer laterally; pleural areas gray. Wing ratio 0.42; costal vein ratio 0.41; M vein ratio 0.54. Femora gray with extreme apex yellowish, medial surface of hindfemur shiny, reddish yellow; tibiae mostly yellowish with some sparse whitish to whitish gray microtomentum, especially hindtibia medially; tarsi yellow. Abdomen: Tergites 2-4 with wide medial stripe bronzish brown, gray laterally; tergite 5 mostly gray, truncate apically, bearing 4 larger apical setulae, length of larger setulae equal to width of tergite at apex. Male terminalia : Epandrium in posterior view (Fig. 200) more or less cordate, wide on dorsal half, tapered ventrally to a narrow, truncate ventral apex, dorsal margin broadly connected, width of dorsal connection in lateral view equal to width of a cercus, epandrium in lateral view (Fig. 201) becoming widest at midheight, thereafter tapered to point ventrally; cercus semi-hemispherical in posterior or lateral views ( Fig. 200-201), height about twice width, overall height about ⅓ length of epandrium; phallapodeme and aedeagus fused, in ventral view (Fig. 202) rectangular, lateral margins parallel sided, apex truncate, base rounded, in lateral view (Fig. 203) as a fish tail apically; gonite in lateral view (Fig. 203) broadly bifurcate with dorsal and posterior prongs, both narrow, digitiform, ventral prong slightly longer and more robust, in ventral view (Fig. 202) rod-like, shallowly curved, with a midlength, short, bud-like prong. Type material. The holotype male of Hecamedoides ceraceps Cresson is labeled "551/TYPE Hecamedoides CERACEPS E.T. Cresson,Jr. [red; species and generic names handwritten]." The holotype is double mounted (minuten in a rectangular block of pith), is in good condition (some vertigis near exit and entrance of minuten; some mesonotal setae broken; abdomen removed and dissected with the parts in an attached microvial of glycerin), and is deposited in the ANSP (6534).
Type locality. "BRAZIL." Remarks. This species and D. buccata are apparently closely related, as evidenced by the high gena, which is unique within Discocerina and which was also the reason why both species had been placed in Hydrochasma. Like D. buccata and other congeners in Discocerina, however, D. ceraceps has the phallapodeme fused with the base of the aedeagus, a synapomorphy for these species and other congeners in Discocerina.