The New World whirligig beetles of the genus Dineutus Macleay, 1825 (Coleoptera, Gyrinidae, Gyrininae, Dineutini)

Abstract All New World members of the whirligig beetle genus Dineutus Macleay, 1825 are treated. The New World Dineutus are found to be composed of 18 species and 6 subspecies: one species, Dineutus mexicanus Ochs, 1925, stat. n. is elevated from subspecies to species rank, and the subspecies Dineutus carolinus mutchleri Ochs, 1925, syn. n. is synonymized here with the typical form. Lectotypes are designated for Dineutus discolor Aubé, 1838, Dineutes metallicus Aubé, 1838, Dineutus solitarius Aubé, 1838, Dineutes analis Régimbart, 1883, and Gyrinus longimanus Olivier, 1795. Each taxonomic unit is provided with a taxonomic history, type locality, diagnosis, distribution, habitat information, and a discussion section. The aedeagus and male mesotarsal claws are illustrated, and dorsal and ventral habitus images of both sexes, for each species and subspecies are provided. General distribution maps are provided for all taxonimc units. A key to the genera of New World Gyrinidae, as well as all the New World Dineutus species is provided. General Dineutus anatomy as well as a clarification of homology and anatomical terms is included.


Introduction
The genus Dineutus Macleay, 1825 is represented in the New World by 18 species and 6 subspecies. Members of Dineutus are among the largest of all New World whirligig beetles found in North and Central America, where they are common elements of aquatic environments including ponds, lakes, rivers, and streams. The genus is known from tropical regions around the world, but is notably absent from South America (Miller and Bergsten 2012). There have been several previous treatments of New World Dineutus, most of which were regional: Leech (1948) treated California; Ochs (1949), Central America; Young (1954) and Epler (1996;, Florida; Gordon and Post (1965), North Dakota; Sanderson (1982) for North and South Carolina; Ferkinhoff and Gunderson (1983) for Minnesota and its adjacent states and Canadian provinces; Hilsenhoff (1990) for Wisconsin; and Ciegler et al. (2003) for South Carolina. The largest published treatments of the genus Dineutus for North America were only for the region north of Mexico by LeConte (1868) and Roberts (1895). Since these works there has been no comprehensive treatment of the genus published and readily available for all of the New World. Wood (1962) did treat all Dineutus of the western hemisphere, however, his master's thesis was never published and portions heavily relied on previously published work for treatment of the more uncommon species. The main purpose of this project is to treat, for the first time, the entire Dineutus fauna of the New World, including all known species and subspecies, and the elevation of one subspecies to species status.
Classically, the genus Dineutus in the New World was divided into two subgenera: Cyclinus Kirby, 1837 and Dineutus sensu stricto by Hatch (1925bHatch ( , 1930 and Ochs (1926a;1949). This division was primarily based on the overall body form, with Cyclinus comprising the smaller, more elongate and narrowly oval species, with the large and broadly oval species placed in Dineutus s. str. The lack of concrete characters and seeming continuum of body sizes has been an issue discussed in the past by Hatch (1925b), and the difficulty in separating these subgenera convincingly from the African subgenus Protodineutus Ochs, 1926b was noted by Brinck (1955), without any resolution. Guignot (1950) divided the North American species among four different subgenera, placing most of the species within Cyclinus, moving most of the large and oval species to the subgenus Protodineutus, except D. longimanus (Olivier, 1795) which he placed in the subgenus Rhombodineutus Ochs, 1926b (along with New Guinean species and a Madagascan species) and D. truncatus (Sharp, 1873) which he maintained in Dineutus s. str. Brinck (1955), unsatisfied with Guignot's (1950) classification, instead relegated all North American species to the subgenus Cyclinus without any diagnosis aside from their distribution in North America. To confound matters even more, Miller and Bergsten (2012) recently found that the North American Dineutus species are indeed monophyletic. The phylogenetics of the genus Dineutus, as well as the rest of the dineutine genera and subgenera, will be addressed in a future paper, potentially providing better evidence regarding the monophyly and potential synapomorphies for the North American Dineutus. Until that can be done, we recommend discontinued use of the subgenus name D. (Cyclinus) for the New World species until its monophyly and diagnostic combination can be investigated more thoroughly.
This work is meant to allow for the accurate identification of all the New World species and subspecies of Dineutus. It is our hope that this work will help improve identification of material within public and private collections and help facilitate research on stream ecology, and aspects of these charismatic beetles' behavior and biology. This work greatly improves upon previous identification materials by introducing a novel external character for use in identification (the male mesotarsal claws), providing high-quality habitus photos for each taxon, detailed aedeagal illustrations, distributions maps, and in-depth differential diagnoses.
The vast majority of published research on, or utilising, New World Dineutus species has focused on aspects of their behavior, especially those associated with their water-surface aggregrations. Many of the common Dineutus of North America are known to form giant multispecies and sometimes multigeneric (Realzola et al. 2007) aggregrates of hundreds to thousands of individuals, dubbed rafts by Heinrich and Vogt (1980) (reviewed for all Gyrinidae by Jäch et al. 2010). It is well established that these mass aggregations operate as a selfish herd (Hamilton 1971) for predation avoidance (Romey 1995;Romey and LaBuda 2010;Romey and Rossman 1995;Romey and Wallace 2007;Vulinec and Miller 1989;Watt and Chapman 1998). Several studies have looked at contact behavior of individuals within these aggregates (Freilich 1986;Knight et al. 1996;Vulinec 1987), others at composition of aggregates, daily movements, and changes in aggregate formations and indiviuals' positions (Fairn Evan et al. 2009;Fitzgerald 1987;Freilich 1989;Heinrich and Vogt 1980;Realzola et al. 2007;Romey 1995;Romey and Galbraith 2008;Romey and Wallace 2007). Studies on population dynamics (Nürnberger 1996;Nürnberger and Harrison 1995) and evidence for competition between populations of several broadly sympatric species (Istock 1966;1967) have also been performed. The amazing speed at which gyrinids swim, yet maintaining maneuverability (Fish and Nicastro 2003) and avoidance of collisions within aggregates (Romey et al. 2014) has been of interest more recently. This last aspect is especially interesting as it relates to whirligig beetles' unique antennae's ability to detect surface waves in order to avoid objects (Romey et al. 2014;Tucker 1969). Aspects of gyrinid defensive secretion have also interested researchers, as they produce a unique chemical cocktail, dubbed gyrinidal, which prevents predation (Eisner and Aneshansley 2000;Fitzgerald 1986;Meinwald et al. 1972). Studies on the vision centers of whirligig's have also begun (Lin and Strausfeld 2012;. Nearly all of the above studies have used some of the most common North American species: D. assimilis (Kirby, 1837), D. hornii Roberts, 1895, D. nigrior Roberts, 1895, andD. discolor Aubé, 1838, making it clear Dineutus species present excellent candidates for model study systems for a variety of areas of study.
Despite how common and abundant most species of New World Dineutus are, studies on their life history, and juvenile stages are shockingly missing. The general lack of life history knowledge for all North America water beetles was pointed out as early as the 1920's by Wilson (1923), who provided an excellent general review for most families. There exists no formal study on the complete life history for any species. At most there have been anecdotal accounts of life history scattered about in the literature, or those collected from laboratory reared specimens as part of studies focused on other aspects of the species' biology. Hatch (1925a) described briefly the life history of several common North American species, with much of the data being summarized from other sources. Smith (1926) also added some life history information on D. assimilis in his note on behavior, but this was mostly anecdotal. Istock (1966) briefly describes some life history elements for D. assimilis, D. hornii, and D. nigrior, including adult and larval durations for D. nigrior and D. hornii, later (1967) adding anecdotal pupal information for the later two species, but this was not the focus of Istock's studies. The juvenile stages have similarly never been formally studied and described for any species, with the exception of D. assimilis. Wilson (1923) provided a formal description for all life stages of D. assimilis, including illustrations, and given the date of this work it is quite exceptional. Despite Wilson's (1923) formal description, a modern one is still in order, as there was no incorporation of chaetotaxy. The only other work on the larval form at the species level is that of Hatch (1927), who provided a key to the first instar of four common species. Images of the larvae of D. assimilis, D. hornii, and D. nigrior are provided in Istock (1967), without information as to which instar they belong, as again this was not the focus of the paper. Keys to the larvae of North America gyrinid genera have been provided, with the exception of Spanglerogyrus Folkerts, 1979, for which larvae remain unknown (Sanderson 1982;White and Roughley 2008). Hopefully accurate identification of species will facilitate much needed research on life history and juvenile stages in New World Dineutus.

Material and methods
A total of 1674 specimens were examined for this study. Specimens were loaned in order to have each species represented for study, as the goal of this paper is to make identification possible, and to summarize available information on the New World species. This study is not meant to be a revision of the genus in North America, thus no attempt was made to obtain all available material. Material was loaned until all known species were represented for study, thus material was not loaned from some of the larger collections like the Smithsonian Institution (United States National Museum, Washington, D.C., U.S.A), as it was not necessary in order to have all species accounted for in this study. The second author has visited the Smithsonian Institution and confirmed loaning of their large quantity of material, would likely only add more locality data, at the risk of damaging specimens.
For each species a taxonomic history is provided. This list is a partial chresonomy sensu Dubois (2000) meant to track origins of incorrect subsequent spellings, synonyms, and changes in taxonomic rank or movement for each name. The list is not a complete logonomy or chresonomy in that every single use of the name is not tracked, but instead the list provides efficient taxonomic information for the history of the name. The family-group name classification follows Gustafson and Miller (2013).
Measurements were taking using a Cen-Tech 4 inch Digital Caliper (ITEM 47256). Total body lengths were measured from the anterolateral margin of the clypeus to the apex of the elytral apices. These areas were chosen for the boundaries of lengths since they are more fixed than other possible boundaries. For example, the labrum may be depressed thereby making it a poor choice as an anterior boundary, and the abdomen may be more or less protruding making it an unsuitable posterior boundary. For each species and subspecies an attempt was made to measure the largest and smallest specimens available for each sex.
Specimens for dissections and imaging were relaxed by placing them in lightly boiling water.
The aedeagus was then dissected from relaxed males and placed in warm 10% KOH for about 5 minutes. Following removal from KOH the aedeagus was placed in vinegar to neutralize the base and washed in water. After dissection and/or imaging aedeagi were placed in microvials attached to the pin with the original specimens.
Images of non-aedeagal structures were drawn using a camera lucida attached to a Zeiss Discovery V8 stereo microscope. For aedeagi, drawings were made using Adobe Illustrator by tracing and modifying light photography images subsequently modified in Adobe Photoshop.
Dorsal, ventral habitus as well as aedeagal images were taken using a Visionary Digital BK+ light imaging system (www.visionarydigital.com, R. Larimer).
Handwriting on type labels was identified using Horn et al. (1990). Specimens examined were loaned or examined from the following depositories:

On the homology of the gyrinid anatomy and terminology
In many groups of aquatic beetles morphological structures, especially the legs, have been rotated, and maintaining appropriate homology relative to other groups of beetles is critical (Miller and Nilsson 2003). Within the Gyrinidae the current position of all the legs are different from the ancestral condition within Adephaga. Gyrinidae have their prothoracic legs rotated ca. 90° anteriorly in normal anatomical repose, whereas the meso-and metathoracic legs have been rotated ca. 90° posteriorly, similar to the condition in Dytiscidae (Miller and Nilsson 2003). Therefore, the surfaces homologous with other beetles have changed such that what appears to be the "ventral" and "dorsal" surfaces are actually the anterior and posterior surfaces in the meso-and metathoracic legs (Miller and Nilsson 2003). Similarly the "true" ventral and dorsal surfaces are now located "posteriorly" and "anteriorly" in the meso-and metathoracic legs. Both situations are reversed in the prothoracic legs, which have been rotated in the opposite direction relative to the meso-and metathoracic legs. Previous gyrinid workers (e.g. Brinck 1955) have not used terminology reflecting the homologous surfaces, but we here follow Miller and Nilsson's (2003) suggestion to use terminology more carefully reflecting this.
Other terminology referring to gyrinid morphology largely follows that of Lawrence et al. (2011), Brinck (1955 and Roberts (1895). A detailed illustration of Dineutus morphology and terminology used here is provided in Figs 1 and 2. There are seven visible adominal ventrites in Dineutus, however, the roman numerals given in Fig. 1B refer to the true homologous abdominal sternite count, with the first sternite being hidden by the metacoxae (Lawrence et al. 2011). While it appears that there are actually only six visible ventrites, the first visible ventrite is actually two fused sternites (a suture is still visible in some taxa such as species of Enhydrus (Brinck 1955;Miller and Bergsten 2012)).

Structures of taxonomic importance
The purpose of this paper is to allow for the identification of all the species of Dineutus within the New World. A key to the genera of Gyrinidae within the New World as well as to all the species of Dineutus is provided. The key to species works for both males and females. The identification of Dineutus can be done without many difficulties using only external characters. However, several characteristics of the genus make identification somewhat difficult. First, males and females tend to be dimorphic with the females of several species appearing very similar (e.g. D. assimilis, D. nigrior, and D. hornii). Whereas gyrinids are often collected in large rafts or aggregrates, these aggregates often contain multiple species or even multiple genera (Realzola et al. 2007). Therefore, each specimen may need to be identified carefully to avoid assuming all belong to the same species. Furthermore, many species are separated by very minor external characters, but differ drastically in genitalia. Therefore the dissection of genitalia is often required for reliable identification and may require dissection of multiple specimens from a series to ensure all species within the aggregation are identified correctly. For this reason, for each species, a dorsal and ventral habitus are included of both sexes, as well as illustrations of the aedeagus and the male mesotarsal claws.
Mesotarsal claws (Fig. 1B mscl): The mesotarsal claws of New World Dineutus are sexually dimorphic, a feature that has been overlooked in previous treatments of the group. Males have the mesotarsal claws modified in several ways causing them to differ significantly from the metatarsal claws, whereas the mesotarsal claws of females are more similar in form to the metatarsal claws in terms of size and shape. The mesotarsal claws of females do differ from the metatarsal claws, however, not to the degree of the male's. The modifications to the male mesotarsal claws include increased size (Fig. 32C), the presence of a denticle on the ventral margin of one or both claws in some species (Fig. 36C), and variations in the curvature of the ventral margin of the claw, from straight ( Fig. 17C) to strongly curved (Fig. 21C). The mesotarsal claws are useful as an external diagnostic character to distinguish between several externally similar species such as D. assimilis (Fig. 9C) and D. nigrior (Fig. 32C).
Protibial shape (Fig. 1B prtb): The overall shape of the male protibia has been historically used as a diagnostic character (Roberts 1895;Wood 1962;and Ochs 1949) and is used here, though it is not always diagnostic. This is another sexually dimorphic character. Males typically have a variety of protibial shapes, whereas females most often have a more generalized club-shaped protibia. There are three protibial shapes seen in New World Dineutus: club-shaped, wedge-shaped, and subsinuate. Club-shaped is the most general of the protibial shapes, and is characterized by more or less similar protibial width throughout the entire protibial length (Fig. 44C, D), or the protibia is only weakly expanded distally (Fig. 14C, D). This shape occurs in most of the Central American and Mexican species, as well as in the female of the majority of species. The wedge shape is represented by a more or less even expansion distally and is exemplified by males D. assimilis (Fig. 8C), D. nigrior (Fig. 31C), and D. hornii (Fig. 18C). The subsinuate shape is represented by the protibia with the medial margin more or less abruptly expanded distally with the proximal half of the protibia narrow and parallel sided. Species exemplifying this modification are D. productus (Fig. 33C) and D. serrulatus serrulatus (Fig. 40C).
This character is another case of sexual dimorphism, present only in males. An exception to this may be D. amazonicus Hatch, 1930, which is characterized by the presence of a profemoral sub-apicoventral tooth in females. For more discussion on the enigmatic D. amazonicus see the discussion section for that species.
There are other variants of the dentation of the ventral profemora of North American Dineutus. Some species have a second more basal profemoral denticle (i. e. D. longimanus), but for the purpose of this study only the sub-apicoventral denticle, referred to through the rest of this paper as the profemoral sub-apicoventral tooth, was used for diagnostic purposes, as the development of the more basal denticles varied noticeably within species. One species, D. productus, has a unique dentation consisting of a series of denticles along the femoral margin with each denticle associated with a setigerous puncture, and the sub-apicoventral tooth distinct.
Elytral apices (Fig. 1A elap; Fig. 3): The elytral apices are highly diagnostic for North American Dineutus (Fig. 3) (Roberts 1895). The elytral apices have two general features of diagnostic importance, the presence or absence of apical serration and/or irregularities, and overall shape. Serration consists of tiny conical cuticular extensions located at the apices of the elytra, usually near the sutural angle and not present laterally beyond the apicolateral angle (Fig. 3E). This serration in some cases is very fine, composed of distinct points, as in D. truncatus, or is reduced to irregularities (bumps, weak cones, or projections resulting in an irregularly non-smooth edge), as in D. mexicanus or D. productus, with the character varying both within and among populations. Some species never have serrations and/or irregularities present.
The general shape of the elytral apices is also diagnostic of groups of species. In some species, the elytral apices are simple and evenly rounded (Fig. 3A) characteristic of D. carolinus (Fig. 10A,C) and D. emarginatus (Fig. 19A,C). Another form of rounded elytral apices is present, where the apex is much more flatly rounded, as opposed to regularly evenly rounded, which is referred to here as flatly rounded (Fig. 3B). This flatly rounded apex, sometimes has a near truncate appearance, for which it is also referred to as subtruncate. Species exemplifying the flatly rounded/ subtruncate elytral apices are D. sublineatus (Fig. 44A), D. discolor (Fig. 14A), and D. serrulatus serrulatus (Fig. 40A) The most common modification of the elytra is to have the sutural angle produced into a broad triangular point (Fig. 3C) as in D. productus (Fig. 33A) and D. nigrior (Fig. 31C). This production can be variable from nearly totally reduced to well evident. When variable, examination of other diagnostic character states may be required for identification. The more modified elytral apices are truncate (Fig. 3D) or spinose (Fig. 3E). Truncation is only truly present in D. truncatus (Fig. 47A, C) and D. mexicanus (Fig. 28A,C) and spinosity is present in D. longimanus (Fig. 20A,C). Several of these conditions are accompanied by serration as described above.
Venter coloration: The coloration of the ventral surface is another important diagnostic character (Roberts 1895). Most New World species of Dineutus have the ventral surface dark, usually dark reddish brown to dark brownish black in coloration. However, several species have the venter lightly colored from yellowish orange to red.  . Elytral apex types of North American Dineutus. A regularly rounded, without apicolateral sinuation B flatly rounded/sub-truncate, with apicolateral sinuation C sutural angle produced, with apicolateral sinuation D truncate, with serrationb E spinose, with serration.
Antennal shape (Fig. 1A ante): The shape of the antennae is useful for identification with overall thickness and appearance of the ultimate antennomere useful for distinguishing very similar species like D. hornii and D. assimilis, especially when comparing female specimens. But in general antennal shape alone is not diagnostic. Aedeagus (Fig. 2): For this study the male aedeagus was considered to be an important indicator of species boundaries. The male aedeagus is by far the best diagnostic feature for species identification of North American Dineutus. Most species have clear and easily distinguishable characters associated with the aedeagus, including the shape of the median lobe, the shape of the sperm-groove, and the shape of parameres. The aedeagus is best viewed in the dorsal aspect ( Fig. 2A) for most diagnostic features, such as acumination of the apex of the median lobe, whereas the ventral aspect ( Fig. 2B) is used much less frequently for comparison between species' sperm-grooves ( Fig. 2B spmg). The lateral view can be quite informative for determination of species where the apex is dorsally curved (e.g. D. nigrior Fig.  32D). The aedeagus should not be viewed nor kept dried as the shape of the median lobe becomes distorted, and should be maintained in a microvial with glycerin and viewed in water. Dissection and examination of the male genitalia is the best means for identification of species.
Setigerous profemoral punctures (Fig. 1B prfs): In the past, the number of setigerous profemoral punctures present on the anterior surface of the prothoracic legs has been used as a diagnostic character for separating species (Roberts 1895;Ochs 1924Ochs , 1929Young 1954). However, as has been previously found (Wood 1962), these characters are not useful diagnostically. Species vary in the number of setigerous punctures, especially in those that have a large degree of size variation, with larger specimens tending to have an increased number relative to smaller specimens. Further, the setae are often lost and the punctures themselves can be difficult to see in dirty specimens. For these reasons, the number of setigerous profemoral punctures is not used here. There is also a row on the posterior surface of the profemora, but, similarly, these were found to be unreliable as diagnostic features.
Dorsal coloration: The dorsal coloration of North American Dineutus varies from olive green in color, to metallic bronze, but most species are black to dark green. Although there are some differences in dorsal coloration, the diagnostic utility of this feature is not great. In North American Dineutus examined, there occur specimens of both sexes that are much more darkly colored, usually appearing black, even in species normally olive-green in dorsal color. These "melanized" forms occur across the species and, as such, there are specimens in all species that are not diagnosable using color. This melanization occurs naturally (noticeable even in the field during collection) and is not a result of preservation. For this reason, dorsal coloration is described but is not used as a comprehensively diagnostic feature. Elytral apices modified, having the sutural angle produced into a more or less developed point (Fig. 3C), rarely rounded or flatly rounded/sub-truncate and without point: if rounded and/or flatly rounded and without point, then protibiae wedge-shaped (Fig. 8C), not club-shaped (Fig. 12C), epipleuron of elytra similar in color as adjacent thorax and abdomen, never lightly colored orange or yellow, and metallic sheen often present. No apical serration present, at most some irregularities or wrinkles; mesotarsal claws either noticeably asymmetrical or with claws similar in size but with the ventral margins straight; not with claws similar in size with ventral margins shallowly curved, nor with a denticle .  . 18C), attenuated anteriorly; medium size: 9.9-10.9 mm. Protibiae wedge-shaped, not club-shaped; Elytra without a bronzy lateral stripe ending before elytral apex; venter darkly colored (Fig. 18D) usu-ally dark reddish, rarely with a metallic luster, if metallic luster present then it is weakly developed, epipleuron lighter in coloration, usually yellowish orange (Fig. 18D); mesotarsal claws ( Fig. 19C) similar in size and noticeably larger than metatarsal claws, ventral margin shallowly curved, not straight, and without denticle. Aedeagus (Fig. 19A, B, D) with median lobe in dorsal view mostly parallel sided, evenly narrowed in apical 1/3, apex strongly narrowed, in lateral view apex of median lobe weakly curved dorsally; parameres in dorsal view laterally expanded in apical 1/4, nearly evenly rounded apically. Southeast Canada and eastern half of the United States ....... Dineutus hornii 6 (5)
Distribution. Known only from the type locality.
Habitat. Unknown Discussion. Dineutus amazonicus was described from a single female specimen collected in Arkansas during the 1930's. The species, as described by Hatch (1930), is unique among all other North American Dineutus in having females with an subapicoventral tooth present on the profemora, running approximately 1/5 its length. In Dineutus this is a commonly sexually dimorphic character, with the tooth present only in males. Hatch (1930) indicated the elytra of this species are similar to those of D. emarginatus, being regularly rounded and lacking serration.
We were unable to locate the type specimen either at the Smithsonian (F. Shockley, pers. comm.) or Oregon State University (C. Marshall, pers. comm.) where Hatch's collection was deposited. No specimens in the University of Arkansas collection were identified as D. amazonicus (J. Barnes, pers. comm.). It appears that the type may be missing, and that no other published records of this species have occurred since its description in 1930. Although Hatch's (1930) description at first sounds dubious, as the profemoral sub-apicoventral tooth is in all other species unique to males, Hatch was unlikely to mistake a female gyrinid for a male (Hatch 1925b(Hatch , 1926, and it therefore seems unlikely that he described a merely aberrant form. For this reason we have included the enigmatic D. amazonicus, without having seen neither type nor any other specimens of this species. The first author recently visited the type locality in an attempt to recollect this species, but was unsuccessful. The locality, Saline River, a large mud bottom river, also had present D. ciliatus as described by Hatch (1930), but unsettlingly, the only other species collected at this locality was D. emarginatus, the species stated to be most similar to that of D. amazonicus. Hopefully in the future the type may be rediscovered or this enigmatic species recollected and its relationship with D. emarginatus clarified.  10-18.v.1985, leg Diagnosis. Male ( Fig. 4C-D): Size: 8.7-9.3 mm. Body form elongate oval; elytral apices with sutural angle produced to a point, with serrations and irregularities present apically, elytra with reticulation very strong laterally, medial disc with reticulation sparse or absent, striae often not apparent, lateral marginal depression of elytra not present; profemora with small sub-apicoventral tooth; protibiae club-shaped with apicolateral margin obliquely angled; mesotarsal claws ( Fig. 5C) with ventral margin weakly rounded; venter darkly colored, reddish brown to black, weakly metallic, mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen; Aedeagus ( Fig. 5A, B, D) median lobe in dorsal view shorter than parameres, nearly parallel sided, narrowed in apical 1/6; parameres weakly expanded laterally in apical 1/3, medially weakly curved, flatly rounded apically. Female ( Fig. 4A-B): Size: 8.9-9.1 mm. Body form elongate oval; elytral apices with sutural angle produced, with serrations and irregularities present apically, apicolateral sinuation present, elytra with reticulation strongly present laterally, medial disc with reticulation sparse or absent, striae often not present, lateral marginal depression of elytra absent; profemora without sub-apicoventral tooth; protibiae club-shaped with apicolateral angle rounded; venter darkly colored, reddish brown to black, weakly metallic, mesothoracic and metathoracic legs and apex of abdomen usually lighter in coloration.

Dineutus americanus
Differential diagnosis. Dineutus americanus is unique among all other species of Dineutus in North American in having an elongate oval body form (Fig. 4A, C), elytra without a well defined marginal depression, strong lateral reticulation, with striae mostly absent, the elytral apices with the sutural angle produced to a point with apical serrations and irregularities present, in the male having the profemora with a small sub-apicoventral tooth, protibiae that are club-shaped, and in the form of the male aedeagus (Fig. 5A). This species is also unique in being small in size and endemic to the Caribbean, reaching the Florida Keys (Fig. 55A). The species most similar to D. americanus is D. carolinus.
Both sexes of D. americanus can be distinguished from D. carolinus in having the sutural angle of the elytra produced to a point and being generally smaller in size. However, this production can sometimes be highly reduced to only a small point at the sutural angle, especially in males. Both sexes of D. americanus can further be separated from D. carolinus in lacking the marginal depression of the elytra seen in D. carolinus. The absence of the elytral marginal depression is most evident in the humeral region of the elytra, where in D. carolinus it is steep and narrow, becoming larger and shallower posteriad. Dineutus americanus has the elytra more evenly convex with the lateral portions of the disc with a very strongly impressed reticulation, producing a bronzy green appearance. The elytra also often do not have the striae very apparent due to the strong reticulation, whereas the striae are often faint but evident in D. carolinus.
The aedeagus (Fig. 5A) will unambiguously distinguish males of D. americanus from D. carolinus. In D. americanus the median lobe ( Fig. 5A) is weakly constricted medially, and only narrowed in the apical 1/6 of its length, whereas that of D. carolinus ( Fig. 11A) is parallel sided for much of its length, fairly evenly narrowed in the apical 1/3, and is much more narrow overall. The parameres also differ, with those of D. americanus more curved along both lateral and medial margins.
Females of D. americanus can be distinguished from D. carolinus by several of the above described differences, but also the elytra are much more noticeably lacking the marginal depression.
Discussion. Many specimens have been misidentified as D. americanus due to a long persisting synonymy issue (see the discussion under D. assimilis). Mistaken records of D. americanus include Ciegler et al. (2003) and Zuellig et al. (2002) for Wyoming and, most likely, the key to larvae provided by Hatch (1927). The true D. americanus is only found in the Caribbean and the Florida Keys (Fig. 55A).
Type designation. Aubé (1838) does not give any exact label data, nor does he mention whose collection the types came from. The syntype series was identified by the presence of a disc on the specimen, which was checked with the registrar present at the MNHN to ensure dates were prior to the description by Aubé. The other specimens present either did not provide dates or had dates after Aubé's (1838) publication. The lectotype ( Fig. 51D) here designated was selected as it had a label present with Aubé's handwriting and identification as "metallicus". We here also confirm that D. metallicus is a synonym of D. americanus as proposed by Schaum (1848).  Co., Branford, 16.vii.1934, leg. J.D. Beamer (4 ex. KSEM).

Dineutus angustus
Diagnosis. Male ( Fig. 6C-D): Size: 9.4-10.8 mm. Body form very narrowly oval, laterally nearly parallel sided; elytral apices rounded with sutural angle produced into a point, rarely with point reduced and elytra appearing completely rounded, elytral apices without serrations and/or irregularities, elytral striae very faint, most evident medially, elytra laterally with strong reticulation, giving a bronzy appearance, medially replaced by fine microreticulation and fine weakly impressed punctures; profemora with small weakly produced sub-apicoventral tooth; protibia weakly club-shaped; venter lightly colored red to reddish orange; Aedeagus (Fig. 7A, B, D) with median lobe in dorsal view parallel sided basally, weakly constricted medially, apically briefly expanded then narrowed in apical 1/4, apex obtusely rounded, in lateral view median lobe narrowed in apical 1/4, in ventral view sperm-groove parallel sided for near entirety of length, apex broadly rounded, parameres very narrow, shortly constricted in basal 1/5, weakly arced in apical half, apically flatly rounded.
Female ( Fig. 6A-B): Size: 9.8-10.2 mm. Body form very narrowly oval, laterally nearly parallel sided; elytral apices roundly angled towards sutural production, with sutural angle produced into a point, apical lateral sinuation often absent, to very weakly developed, elytral apices without serrations and/or irregularities, elytral striae very faint, most evident medially, elytra laterally with strong reticulation, giving a bronzy appearance, medially replaced by fine microreticulation and fine weakly impressed punctures; profemora without sub-apicoventral tooth; protibiae laterally weakly curved, apicolateral margin weakly expanded; venter lightly colored, red to reddish orange. Differential diagnosis. Dineutus angustus is unique among all other North American Dineutus in its small size, parallel sided, very narrowly elongate oval body form ( Fig. 6A, C), light-colored venter, and somewhat in the shape of the aedeagus (Fig.  7A). This species is most similar to D. discolor and it has been debated whether the two are actually distinct species (Régimbart 1892). Dineutus angustus of both sexes can be distinguished from D. discolor by smaller size, as well as the more parallel-sided and dorsoventrally convex body form. However, the aedeagus of the two species are very similar, with some minor differences. Both aedeagi have the median lobe parallel-sided and very narrow parameres. However, in D. angustus the median lobe has a weak constriction medially subtending a slight expansion apically, and a narrowed apical 1/4, whereas the median lobe in D. discolor is nearly parallel-sided for most of the length, with only a very weak constriction medially. The parameres of D. angustus are more curved in the apical 1/3, and accompanied by a weak constriction in the basal 1/5, in comparison to D. discolor which have the parameres much more parallel-sided.
The shape of the apices of the female elytra of D. angustus differs from those of D. discolor. In D. angustus females the apices are broadly angled towards the sutural production and usually lack an apicolateral sinuation. When it is present (rarely), it is only weakly developed. In D. discolor females the elytra are regularly rounded to the sutural production, with an apicolateral sinuation present. Distribution (Fig. 52D). U.S.A., Southern Georgia, and Eastern Alabama to northern Florida (Roberts 1895;Wood 1962;Régimbart 1907).
Habitat. Lotic species, seemingly restricted to highly calcareous streams with a basic pH (Young 1954). For more on habitat preference see discussion.
Discussion. Régimbart (1882) originally considered D. angustus to be a synonym of D. discolor, eventually elevating it to a variation (Régimbart 1892) of D. discolor (comparable now to a subspecies), then eventually accepting it as a species distinct from D. discolor (Régimbart 1902). We have decided to treat D. angustus as a distinct species due to the differences in morphology listed above. The size of the two species in specimens examined for this study only overlap in the extremes, in that the largest specimens of D. angustus only just approach the very smallest of D. discolor. Dineutus angustus was much smaller than any average sized specimen of D. discolor, with only a few female specimens of D. discolor approaching the size of large D. angustus males. Although the aedeagi of both species, which is primarily used here as a delimiter of species boundaries, are very similar, there were some notable differences, even if minor. Young (1954) noticed that D. angustus in Florida appears to be restricted to calcareous streams with a basic pH, while D. discolor appears to inhabit streams with a more acidic pH. Young (1954) mentions "intergrade" forms occuring from streams of intermediate pH with both typical forms of D. discolor and D. angustus present. However, the evidence for the intergrade was in the number of setigerous punctures, which are known to vary among populations, especially with size. Nevertheless, this led Young (1954) to suggest that D. angustus may represent the basic stream ecotype of D. discolor.

Dineutus assimilis
Differential diagnosis. Dineutus assimilis is unique among all North American species of Dineutus in the narrowly elongate oval body form, both sexes with the elytral apices more or less regularly rounded with the sutural angles produced, males with the profemora without a sub-apicoventral tooth, a wedge shaped protibia, mesotarsal claws that are similar in shape with their ventral margins straight, and the form of the aedeagus. The species most similar to D. assimilis are D. hornii and D. nigrior, especially in the form of the females. Males of D. assimilis can be separated from D. hornii by the sutural angle of the elytra being regularly produced to a point, although rarely some individuals have the point reduced giving the elytra a regularly rounded look similar to those of D. hornii. In such cases, specimens of D. assimilis can be distinguished by the elytral epipleura being colored similarly to the adjacent thoracic and anterior abdominal ventrites (Fig. 8D), in contrast with D. hornii in which the epipleura is different in color (much lighter) from the rest of the venter (Fig. 18D). The mesotarsal claws can also be used to separate males of D. assimilis (Fig. 9C) from D. hornii (Fig. 19C). In D. assimilis the ventral margins of the claws are straight, whereas in D. hornii they are very shallowly curved. Dineutus assimilis also have the ultimate antennomere angled, whereas in D. hornii the antennal flagellum is short and thick, with the ultimate antennomere rounded. Males of Dineutus assimilis can be separated from D. nigrior in their smaller size (9.9-11.3 mm), more narrow body form, and, most readily, by the mesotarsal claws which are similar in size with straight ventral margins, whereas in D. nigrior the mesotarsal claws are distinctly asymmetrical with the anterior claw larger than the posterior and both having the ventral margins shallowly curved. The most reliable way to distinguish between D. assimilis, D. hornii and D. nigrior is the aedeagus. The median lobe of the aedeagus of D. assimilis (Fig. 9A) is acuminate in the apical 1/5. The aedeagi of both D. hornii and D. nigrior are more elongate and parallel sided with the median lobe apically narrowed but not acuminate.
Females of D. assimilis are more difficult to differentiate from D. hornii and D. nigrior. Females of D. assimilis differ from those of D. hornii in the epipleura color being similar to the adjacent thoracic anterior abdominal ventrites, whereas in D. hornii the epipleura are lighter in color than the surfaces of the thorax and abdomen (Fig. 18B). The elytral apices of the females of D. assimilis are more similar to those of D. nigrior. In general D. assimilis is smaller (10-11.3 mm) than D. nigrior, and also more narrowed in body form. The most reliable way to separate D. assimilis from D. nigrior is the distal lateral margin of the protibiae. In D. assimilis the distal lateral margin is not produced laterally (Fig. 8B), but continuously weakly curved, whereas in D. nigrior the margin is laterally weakly expanded (Fig. 31B). Distribution (Fig. 52A). Southern Canada from British Columbia to Nova Scotia (Majka 2008;Roughley 1991;Webster and DeMerchant 2012), and east of the Rocky Mountains in the U.S.A. as far south as Texas and Northern Florida (Epler 2010;Ferkinhoff and Gunderson 1983;Folkerts 1978;Gordon and Post 1965;Hilsenhoff 1990;Malcolm 1971;Régimbart 1907;Roberts 1895;Sanderson 1982;Whiteman and Sites 2003;Wood 1962).
Habitat. This is most widespread and commonly encountered species of Dineutus in North America, occupying both lotic and lentic habitats (Woods 1962;Hilsenhoff 1990;Whiteman and Sites 2003). The first author has collected this species in a secondary growth deciduous forest, Baldwin Woods, near Baldwin, Kansas, in a large forest pond with a muddy bottom, with plenty of leaf detritus and several fallen emergent trees. Here D. assimilis was found in large numbers near the shore, with others often exploring deeper regions of the pond. In New Brunswick, Canada, D. assimilis was collected in similar habitats, the margins of ponds with emergent vegetation within forests composed of red oak and red maple (Webster and DeMerchant 2012). Webster and DeMerchant (2012) also found D. assimilis in black spruce and tamarack bogs. This species has also been collected in other lentic situations from the Prairie Region of Missouri, where Whiteman and Sites (2003) found specimens associated with the following plant taxa: Brasneia, Ceratophyllum, Juncus, Lespedeza, Ludwigia, Polygonum, Potamogeton, Sagittaria, Typha, Cyperaceae, and Poaceae. This species also comes to ultraviolet light (Webster and DeMerchant 2012).
Discussion. Dineutus assimilis is the most commonly encountered species of Dineutus in North America, and has one of the largest ranges of any North American species (Fig. 52A), often erroneously listed under the name D. americanus, even recently (e.g. Ciegler et al. 2003). As early as 1927, Ochs (1927b) had the types of D. americanus examined by an associate in London, and determined unambiguously that D. americanus is the Caribbean species, with D. assimilis found in mainland North America. We have again confirmed, after examination of the syntype of D. americanus, that D. assimilis is not D. americanus of Linnaeus. It is likely all records of D. americanus from areas not in the Caribbean or the Florida Keys actually represent D. assimilis. An example of references clearly referring to D. assimilis is Zuellig et al. (2002), who recorded "D. americanus" from Wyoming. Hatch's (1927) key to the larvae of "D. americanus" most likely refers to D. assimilis as well.
Female ( Fig. 10A-B): Size: 8.7-10.6 mm. Body form elongate oval; elytral apices regularly rounded, with serrations and irregularities present apically, apicolateral sinuation usually present, sometimes very strongly developed, elytra with reticulation strong laterally and apically, medial disc with reticulation sparse or absent, striae faintly present, most evident medially on elytral disc, lateral marginal depression of elytra evident, narrow in humeral region, expanded posteriad, usually extending to lateral elytra apex; profemora without sub-apicoventral tooth; protibiae weakly subsinuate, distolateral margin flatly angled; venter darkly colored, reddish brown to black, mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen.
Differential diagnosis. Dineutus carolinus is unique among North American Dineutus in having both sexes elongate oval and the elytra with a distinct lateral marginal depression, the elytral apices regularly rounded with serration and irregularities present, males with the profermoral sub-apicoventral tooth small and often atop a short carina, the male mesotarsal claws with the ventral margin rounded, and the unique shape of the aedeagus. The species most similar to D. carolinus are D. emarginatus, D. solitarius, and D. americanus.
Both sexes of D. carolinus can be separated from D. emarginatus by the elytra apices being more narrowly rounded with serrations and/or irregularities present. The presence of serrations, however, can be variable. In some individuals it is somewhat evident at the sutural margin, but others lack serrations entirely, having only roughened irregularities. The microreticulation of the elytra of D. carolinus tends to be much more coarse laterally and the medial disk of the elytra often lacks reticulation, whereas D. emarginatus tends to have fine microreticulation covering the entire elytra. Although not as reliable, the ventral coloration differs between the two species. In D. carolinus the entire venter tends to be more reddish brown whereas it is regularly black in D. emarginatus. The dorsal coloration of the two species is very similar.
Males of D. carolinus can fairly easily be separated from D. emarginatus by the profemoral sub-apicoventral tooth small atop a profemoral carina, rather than large and triangular. Also, in D. carolinus the mesotarsal claws have the ventral margins rounded, rather than straight as in D. emarginatus. The aedeagus is the best way to identify D. carolinus. The median lobe of D. carolinus is regularly narrowed for much its length, until the apical 1/3 where it is more strongly narrowed, but not strongly acuminate as in D. emarginatus. Females of D. carolinus are more difficult to separate from D. emarginatus. The best way to distinguish them aside from the more narrowly rounded elytral apices with serrations and/or irregularities in D. carolinus is the presence of an apicolateral sinuation in the elytra. This sinuation is nearly always present and well-developed in D. carolinus, although in some females it is sometimes weakly developed or absent. Dineutus emarginatus females nearly always have this sinuation absent, but at most only weakly developed.
Members of Dineutus carolinus of both sexes can be distinguished from D. solitarius by more elongate oval body form, the pronotum more narrow with the lateral margins more narrowly angled basally to apically, and the elytral apices more narrowly rounded apically with serrations and irregularities present. Dineutus carolinus of both sexes also have the lateral marginal depression of the elytra present, which is not evident in D. solitarius. Males of D. carolinus differ from those of D. solitarius by the mesotarsal claws with the ventral margin curved, unlike D. solitarius that have the ventral margins straight. The aedeagus of D. carolinus is tapered but not acuminate, whereas that of D. solitarius is acuminate. Females of D. carolinus can also be separated from those of D. solitarius by the apices of the elytra laterally sinuate, whereas in D. solitarius they are usually evenly rounded without an apicolateral sinuation, and if a sinuation is present, it is very weakly developed.
Dineutus carolinus can be separated from D. americanus by the differences provided under the differential diagnosis for D. americanus. Distribution (Fig. 53A). Mainly known from the southeastern half of the United States (Epler 2010;Folkerts 1978;Régimbart 1907;Roberts 1895), as far south as the extreme northeast corner of Mexico (Wood 1962), and east into the Caribbean where it is primarily known from Nassau (Young 1953), the range is here extended to the southeast as far as Great Exuma Island.
Habitat. This species appears to be primarily lentic (Young 1953(Young , 1954. Dineutus carolinus occurs in Florida and is characteristic of small upland and flatwoods ponds, only rarely being found in slow streams with ample vegetation (Young 1954). The first author has collected D. carolinus in slow moving mud bottomed streams and bayous in southeastern Texas.
Discussion. Dineutus carolinus is the only species of Dineutus well established across much of continental North America as well as in the western Caribbean where its range overlaps with that of D. americanus. The two species are fairly similar.
The Caribbean subspecies D. c. mutchleri was described by Ochs (1924), from Nassau (Bahamas), who used several characters to separate it from the mainland subspecies including, size and number of setigerous femoral punctures, as well as aedeagal shape. Size shows overlap and is not discrete. Number of setigerous punctures is known to vary among populations, especially with size (pers. obs.; Wood 1962). Ochs (1924) described differences in the aedeagus comparing it to the illustration provided by Roberts (1895), but the aedeagus of specimens examined from the Bahamas are identical to that of the mainland populations. We found the aedeagus of the Bahaman specimens to be nearly identical to those from mainland Florida and elsewhere (Fig. 11). Young (1953) also noticed the similarity and suggested that the drawing by Roberts (1895) was actually from an undescribed form in Texas. Ochs (1929) also mentions having compared the Bahaman specimens of D. c. mutchleri to specimens of D. carolinus from Texas, and that those showed greater differences than the Bahaman form.
Having examined some specimens of D. carolinus from Texas (FSCA) there is some variation, but not much from other populations of D. carolinus. A single male specimen examined from Texas has minor variation in the aedeagus from other mainland specimens (Fig. 11H), which may explain Roberts (1895) illustration. This specimen has the apical 1/3 of the median lobe more strongly narrowed (Fig. 11H) than other populations of D. carolinus ( Fig. 11A-E, G) from the mainland. The median lobe of the Texas D. carolinus is nearly as long as the parameres, which are very parallel-sided and flatly rounded, similar to other populations of D. carolinus (Fig. 11). Although Roberts (1895) illustration shows the strong narrowing, it also indicates the median lobe shorter than the parameres, which is not the case in our specimen. The parameres in Roberts (1895) illustration, however, match well with our specimen. Therefore, it may be that Roberts (1895) drew the aedeagus with the median lobe out of proportion, or, more likely, he drew the median lobe slightly flexed dorsally as happens sometimes during eversion or relaxing of the aedeagus. Externally the male from Texas is very similar to males of other populations. The females of D. carolinus from Texas populations vary more so than male specimens from Texas, when compared to populations outside of Texas. The females are much more broad in appearance, having the pronotal and elytral margins more broadly rounded laterally. In lateral view the females are also slightly more dorsoventrally convex than other D. carolinus females. The increased convexity of the elytra causes the lateral marginal depression to be more shallowly impressed in comparison to other populations. The microreticulation of the elytra also shows variation being much more well-impressed, covering nearly all of the elytra and the pronotum. The elytral apices of Texas D. carolinus females are more broadly rounded and do not have the normal lateral sinuation seen in other populations, but have the apices laterally angled or simply regularly meeting the rounded apices, and the apical serrations and irregularities are highly reduced although, under careful observation, present. All of these variations, however, are well within the typical range of variation within other species of Dineutus and it is our judgment that the populations from Texas are not differentiated enough to merit a formal taxonomic name. The specimens examined from Texas were from the southeastern part of the state, in Montgomery County, near The Woodlands, north of Houston (FSCA). Ochs (1929) also admits that after having examined more D. carolinus from Florida and Georgia, that D. c. mutchleri are much more similar to these populations of D. carolinus than the Texas forms which he used as a comparison during description of D. c. mutchleri. It does appear that the Texas specimens are the most distinctive of D. carolinus populations, and the populations from the Caribbean formally named as a subspecies by Ochs (1924) are not, in fact, particularly distinctive. Therefore, based on examined specimens from Texas, southeastern U.S., and the Caribbean, we consider Dineutus carolinus mutchleri as a junior subjective synonym of Dineutus carolinus. Type locality. East Indies, likely in error. The type is labeled, "Ind." according to Ochs (1949), which Young (1954) Amherst, 16.vi.1904 (1 ex. MTEC); Norfolk Co., Blue Hills Reservation, v.1929, leg. G.C. Wheeler (1 ex. FSCA); New Jersey: Bergen Co., Dumont Woods, 9.iv.1931, leg. C.L. Ragot (1 ex. FSCA); Bergen Co., Woodcliff Lake, 20.v.1934  Diagnosis. Male (Fig. 12C-D): Size: 12.7-14.6 mm. Body form broadly roundly oval; antennal flagellum thick and round, ultimate segment rounded; elytral apices regularly rounded, serration absent, elytra with bronzy lateral stripe disappearing apically, elytral striae weakly developed, 8 th elytral stria without punctures present or strongly evident; profemora without sub-apicoventral tooth; protibiae club-shaped; anterior mesotarsal claw (Fig. 13C) with denticle; venter normally dark reddish brown, rarely reddish orange (teneral individuals); Aedeagus (Fig. 13A, B, D) medial lobe in dorsal view with apicomedial papilla, in ventral view sperm-groove parallel sided, in lateral view median lobe curved, apically narrow, parameres weakly rounded laterally in apical 1/3. Female ( Fig. 12A-B): Size: 11.5-14.6 mm. Body form broadly roundly oval; Antennal flagellum thick and round, ultimate segment rounded; elytral apices regularly rounded, serration absent, elytra with bronzy lateral stripe disappearing apically, elytral striae weakly developed, 8 th elytral stria without punctures present or strongly evident; profemora without sub-apicoventral tooth; protibiae club-shaped; venter normally dark reddish brown, rarely reddish orange (teneral individuals).
Differential diagnosis. This species is most easily distinguished from other members of North American Dineutus by the presence of a bronzy lateral stripe on each elytron, a regularly oval body form, large size, absence of a profemoral sub-apicoventral tooth in the male, and the form of the male aedeagus (Fig. 13A). Dineutus ciliatus is most similar to D. robertsi, but there are several characters that readily separate the two species. Both sexes of Dineutus ciliatus have the venter dark reddish brown in color instead of light yellowish orange (most evident on the epipleura), the antennal flagellum thicker and rounder with the ultimate segment rounded instead of thinner and more parallel sided with an angled ultimate segment, and the 8 th elytral stria with punctures absent or indistinct. The venter coloration of teneral individuals is lighter, reddish orange, but this does not closely approach that of D. robertsi, which is much more yellow in color. Males of D. ciliatus also have the anterior mesotarsal claws with a more weakly developed denticle on their ventral surface, and a smaller general body size than D. robertsi. The aedeagus (Fig. 13) of D. ciliatus has the median lobe narrow and dorsally curved in lateral view with an apicomedial papilla visible in both dorsal and ventral views. The sperm-groove is much more parallel-sided in D. ciliatus than D. robertsi. Finally, the parameres of D. ciliatus are weakly lateral curved in the apical 1/3 instead of strongly curved as in D. robertsi. Distribution (Fig. 53B). Most of the eastern half of the United Sates (Folkerts 1978;Malcolm 1971;Sanderson 1982;Wood 1962;Young 1954).
Habitat. This is a lotic species (Young 1954;Hatch 1927). In Florida D. ciliatus is commonly found in small, shaded streams, and when found in larger streams prefers to stay near the stream bank (Young 1954). Hatch (1927) describes one habitat of D. ciliatus in Massachusetts as a small sandy bottomed stream, approximately five feet wide and with a depth from six to ten inches, with a flow rate of one foot per second or less. Hatch (1927) also noted that D. ciliatus prefers to reside near the bank of the stream. In east Texas this species was only collected in lotic situations at East Texas Primitive Big Thicket (Realzola et al. 2007). The first author has collected D. ciliatus from both small pebble bottomed forested streams, to larger mud-bottomed rivers, throughout the southeastern United States, where it is quite commonly encountered.
Discussion. Dineutus ciliatus is a common species with a wide range (Fig. 53B) and is frequently collected and represented in collections in large numbers.  Diagnosis. Male (Fig. 14C-D): Size: 10.9-12.1 mm. Body form narrowly oval, attenuated anteriorly; elytral apices rounded with sutural angle produced into a point, rarely with point reduced and elytra appearing completely rounded, apicolateral sinuation present, serrations and/or irregularities absent, elytral striae very faint, most evident medially, elytra with fine microreticulation covering entirety, laterally microreticulation often coarser, medially with fine weakly impressed punctures; profemora with small weakly produced sub-apicoventral tooth; protibia weakly club-shaped, approaching subsinuate in large males, with distolateral margin weakly produced; mesotarsal claw as in Fig. 15C; venter lightly colored red to reddish orange; Aedeagus (Fig.  15A, B, D) median lobe in dorsal view parallel sided basally, weakly constricted medially, weakly narrowed in apical 1/3, apex obtusely rounded, in lateral view median lobe narrowed in apical 1/4, in ventral view sperm-groove parallel sided for near entirety of length, apex broadly rounded, parameres narrow, parallel sided, weakly arced basally to apically, apically very flatly rounded.
Female (Fig. 14A-B): Size: 10.6-12.8 mm. Body form narrowly oval, attenuated anteriorly; elytral apices rounded with sutural angle produced into a point, apicolateral sinuation present, serrations and/or irregularities absent, elytral striae very faint, most evident medially, elytra with fine microreticulation covering entirety, laterally microreticulation often coarser, medially with fine weakly impressed punctures; profemora without sub-apicoventral tooth; protibiae laterally weakly curved, distolateral margin weakly expanded; venter lightly colored, red to yellowish orange. Differential diagnosis. Dineutus discolor is unique among all North American species in the elongate oval and attenuate anteriorly body form, the elytra of both sexes with the apices rounded, with the sutural angle produced to a point with an apicolateral sinuation present, without serrations or irregularities present, a lightly colored venter, and males with the profemora with a small apicoventral tooth, and the form of the aedeagus (Fig. 15A). The species most similar to D. discolor is D. angustus. See the differential diagnosis under D. angustus for separation of the two species. Distribution (Fig. 52D). Extreme southeastern Canada from Ontario to Nova Scotia (Majka and Kenner 2009;Roughley 1991;Webster and DeMerchant 2012), and the eastern half of the United States (Epler 2010;Ferkinhoff and Gunderson 1983;Folkerts 1978;Hilsenhoff 1990;Malcolm 1971;Régimbart 1907;Roberts 1895;Sanderson 1982;Wood 1962), south possibly into Mexico: Durango (Ochs 1949).
Habitat. Dineutus discolor appears to be strictly lotic, inhabiting streams (Ferkinhoff and Gunderson 1983;Hilsenhoff 1990;Webster and DeMerchant 2012), and it has been suggested that this species prefers clear water (Morrissette 1979). In Quebec D. discolor was found in clear running water and in New Brunswick within embayments and along the margins of rivers (Webster and DeMerchant 2012). In Florida, Young (1954) found D. discolor to be a typical inhabitant of small streams in the uplands, avoiding the more acidic streams as well as the true flatwood streams within the state. Within streams D. discolor swims in the current, moving upstream in quick jerks, allowing individuals to maintain their relative position in the stream among their aggregates, and swim downstream to dive and cling to submerged objects when alarmed (Hatch 1925a). In more swift streams D. discolor is often found in eddies behind objects obstructing the current, such as fallen logs, and may be restricted to these habitats (Kolmes 1983a;Vulinec 1987). Stream dwelling Dineutus species also frequent areas where the current is slowed such as pools and wide meanders, avoiding torrential areas, riffles, and more swift currents (Folkerts and Donavan 1973). Members of D. discolor form rafts in areas of flowing water within the streams, with individuals keeping pace so as to remain in position in the raft, and the raft maintains its relative position within the stream (Brown and Hatch 1929;Hatch 1925a). The first author has collected D. discolor in both small pebble-bottomed forested streams as well as large mud-bottomed rivers in the southeast- ern United States. Both situations had clear water similar to situations described above and individuals collected from larger streams were found in areas with slowed water.
Discussion. Dineutus discolor has an extensive range from the northern third of Florida up the Atlantic coast to Canada, and west to Iowa and Minnesota (Fig. 52D). The true extent of the western and southern boundaries of the range of D. discolor seems somewhat uncertain. Ochs (1949) lists a single specimen of D. discolor in his collection as having the label "Mexico, Durango". Kolmes (1983b;1985) discussed the precopulatory behavior of D. discolor describing the interesting "Proleg-up" mate signaling used by females. Kolmes (1983a) also investigated aspects of prey capture within this species.
The larvae of D. discolor have been found under stones within streams with adult D. discolor at a depth of 20 cm to 60 cm in areas where water is flowing, but not so rapidly as to create breaks in its surface such as rapids (Brown and Hatch 1929). Hatch (1927) included D. discolor in a key to gyrinid larvae.
Type designation. While several North American Dineutus specimens carry type designations by "RP Withington III", these were never published thus do not consistute viable nomenclatural acts according to Article 11 of The Code (ICZN 1999). Among the material in the MNHN there are 4 other specimens designated by Withington III as paralectotypes, aside from the specimen here designated formally as the lectotype. Brinck also included a lectotype label on this specimen, but similarly, Brinck did not publish a written account of specimens he designated at the MNHN as lectotypes. The specimen selected here as the lectotype (Fig. 51B) has a locality label indicating the specimen is from the U.S. as well as a disc that allows the date and local to be checked in the MNHN's registrar. Other specimens in the collection (including the unpublished paralectotypes designated by Withington) lack date indications. Therefore only the specimen with the date showing its collection prior to Aubé's description, and being from the United States (as verified by the registrat at the MNHN) is safe to assume was a part of the original syntype series, and is here formally designated as the lectotype of D. discolor. Given the uncertainty of the other specimens suggested to be paralectotypes by Withington III, it is our opinion that these specimens should not be regarded as paralectotypes. Figures 16, 17

Specimens examined. 75
Type material examined. None examined, none available. The Thomas Say entomology collection is known to have suffered substantial damage with portions of his type collection having been destroyed (Mawdsley 1993). Mawdsley (1993) provided a list of the surviving type specimens, but none of Say's gyrinid species appear to remain. The MCZ online type database lists the following specimen as being a "Neotype": (♀, pinned) "340/ ♀/ A. [  Diagnosis. Male (Fig. 16C-D): Size: 8.6-11.0 mm. Body form elongate oval; elytral apices regularly broadly rounded, with serrations and irregularities absent apically, elytra with fine reticulation covering its entirety, striae very faintly present, most evident medially on elytral disc, lateral marginal depression of elytra broad, usually extending to lateral elytra apex; profemora with large triangular sub-apicoventral tooth; protibiae subsinuate; mesotarsal claws ( Fig. 17C) with ventral margin straight; venter darkly colored, usually black to very dark brown, mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen; Aedeagus (Fig. 17A, B, D) median lobe in dorsal view shorter than parameres, medially slightly constricted, acuminate in apical 1/5 producing a strong point, apex very shortly rounded, in lateral view median lobe weakly curved dorsally in apical half, ventrally median lobe with large rounded sperm-groove, parameres in dorsal view rounded laterally at apical 1/3, narrowly rounded apically. Female (Fig. 16A-B): Size: 8.9-10.1 mm. Body form elongate oval; elytral apices regularly broadly rounded, with serrations and irregularities absent apically, apicolateral sinuation usually absent, rarely developed, elytra with fine reticulation covering most of its entirety, striae very faintly present, most evident medially on elytral disc, lateral marginal depression of elytra broad; profemora without sub-apicoventral tooth; protibiae club-shaped; venter darkly colored, usually black to very dark brown, mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen.
Differential diagnosis. Dineutus emarginatus is unique among all other species of North American Dineutus in being elongate oval in body shape, having the elytral apices broadly rounded, without serrations and/or irregularities present apically, males with profemora possessing a large triangular sub-apicoventral tooth, and the shape of the aedeagus (Fig. 17A). The species most similar to D. emarginatus are D. carolinus and D. solitarius. In general D. emarginatus can be distinguished from D. solitarius in being more elongate oval in body form, as opposed to being more regularly oval. This difference is especially evident in the pronotum. D. emarginatus has the lateral margin of the pronotum more straightly angled posteriorly to anteriorly, while in D. solitarius the pronotal lateral margin is more obtusely angled. The shape of the posterior margin of the pronotum differs between the two species, being more sinuate with the lateral portion of the posterior margin of the pronotum angled towards the posterolateral corners in D. emarginatus as compared to the posterior margin being much more straight and less sinuate in D. solitarius. Dineutus emarginatus in general also has a more evident lateral marginal depression of the elytra compared to D. solitarius.
Males of D. emarginatus have a much larger profemoral sub-apicoventral profemoral tooth than do those of D. solitarius, but the species can be unambiguously separated based on the aedeagus. Both species have the median lobe acuminate, however, the acumination differs between the two species. In D. emarginatus the apex of the median lobe is more rounded (Fig. 17A), with the acumination present as a strong point, whose apex is narrowly rounded. The apex of the median lobe of D. solitarius (Fig. 43A) is narrowed towards the acumination, with the acumination also evenly narrowed and highly pointed, with the apex of the acumination appearing sharp and narrow. In overall appearance the median lobe of D. emarginatus is more broad with a shallow medial constriction giving the basal and apical margins of the aedeagus a more sinuous feel, while in D. solitarius the median lobe is more parallel sided and slightly narrowed apically, becoming slightly broadened just before the acumination.
The females of D. emarginatus are primarily distinguished from females of D. solitarius by the general differences listed for separating the two species.
Dineutus emarginatus can be separated from D. carolinus by the differences listed in the differential diagnosis for D. carolinus. Distribution (Fig. 53D). Most of the eastern half of the United States (Régimbart 1907;Young 1954;Wood 1962;Malcolm 1971;Folkerts 1978;Sanderson 1982).
Habitat. Dineutus emarginatus can be found in both lotic and lentic habitats (Young 1954). In Florida D. emarginatus is often found at the mouths of slow moving streams or in lakes in regions where wave action is present (Young 1954). This species can also be found in swamp streams, small sand bottomed streams, and canals with running water (Young 1954). The first author has collected this species form a large man-made lake in the Ozarks of Arkansas, as well as in a large slow moving tributary of a mud-bottomed stream (see the discussion under D. amazonicus).
Discussion. In the past D. emarginatus was divided into two subspecies by Ochs (1929), D. emarginatus s. str. and D. e. floridensis Ochs, 1929. Ochs (1929 based this subspecies on the smaller size of D. e. floridensis from that of the typical form and on the difference in the number of setigerous punctures of the profemora, as well as some minor differences in the body form and elytral shape. This subspecies was also stated to be restricted to peninsular Florida (Ochs 1929;Young 1954) with other populations outside of northern and central Florida being a part of the D. emarginatus s. str. subspecies. Cook et al. (2006) performed a morphometric analysis of several populations of D. emarginatus to assess the claims of a significant difference in size, as that being the main basis for the subspecies D. e. floridensis. Cook et al. (2006) were unable to discriminate between the two subspecies via a morphometric analysis and suggested the synonymy of D. e. floridensis. Ochs (1929) did also mention a difference in the setigerous punctures of the profemora, however as discussed elsewhere, this character is known to be variable.
In a study of gyrinid aggregations at East Texas Primitive Big Thicket by Realza et al. (2007), D. emarginatus was most commonly collected with D. carolinus and also with D. serrulatus analis, but to a lesser extant, but the authors observed that at a given locality both species compositions and proportions were subject to change. Diagnosis. Male (Fig. 18C-D): Size: 9.9-10.9 mm. Body form narrowly oval; antennal flagellum short and thick, ultimate segment broad and round; elytral apices rounded, rarely angled toward suture, elytral striae faintly; profemora without subapicoventral tooth; protibiae wedge-shaped, with distolateral margin straight; mesotarsal claws (Fig. 19C) similar in size, venter darkly colored reddish brown to black, except epipleura lighter in color, yellow to orange; Aedeagus (Fig. 19A, B, D) median lobe in dorsal view mostly parallel sided, evenly narrowed in apical 1/3, apex strongly narrowed, flatly rounded, in lateral view apex of median lobe weakly curved dorsally; parameres in dorsal view laterally expanded in apical 1/4, nearly evenly rounded apically, in ventral view sperm grove narrow and parallel sided for most its length. Female ( Fig. 18A-B): Size: 10.3-11.3 mm. Body form narrowly oval; antennal flagellum short and thick, ultimate segment broad and round; elytral apices produced, angled towards sutural production, sutural angle produced into a point, apicolateral sinuation present, elytral striae faint basally and laterally, mainly evident apicomedially, becoming more evident apically and laterally; profemora without sub-apicoventral tooth; protibiae laterally weakly curved, distolateral margin weakly expanded; venter darkly colored, reddish brown to black, except epipleura lighter in color, yellow to orange. Differential diagnosis. Dineutus hornii can be distinguished from all other North American species of Dineutus in having the epipleura light yellow to orange, while still having a darkly colored venter (as opposed to similarly lightly colored as in D. discolor) (Fig.  18B, D), and the males by the form of the aedeagus (Fig. 19A). The species most similar to D. hornii are D. assimilis and D. nigrior especially the female forms. But both sexes differ from the following two species in having the epipleura (Fig. 19B, D) lightly colored yellow to orange relative to their darker venters, as well as having antennal flagella that are short and thick with the ultimate segment appearing broad and round. In both D. assimilis and D. nigrior the epipleura is similarly darkly colored like the rest of the venter, and in D. assimilis often accompanied with a metallic sheen. The ultimate segment of the antennal flagellum in both species differs in being angled as opposed to rounded as in D. hornii.

Dineutus hornii
Males of Dineutus hornii can be readily distinguished from both D. assimilis and D. nigrior in having the elytral apices rounded (rarely angled towards the suture) and without the sutural angle produced to a point (Fig. 18C). The aedeagus (Fig. 19A) of D. hornii is more similar to D. nigrior (Fig. 32A), but can distinguished by the median lobe in dorsal view being more parallel sided, being evenly narrowed in the apical 1/3 (as opposed to apical 1/4), and having the apex of the median lobe flatly rounded at the tip. The median lobe also differs from D. nigrior in having the apex weakly curved dorsally in lateral view (Fig. 19D) as opposed to strongly curved in D. nigrior (Fig.  32D). The pararmeres of D. hornii differ from those of D. nigrior in being expanded laterally in the apical 1/4, and evenly rounded apically, and in lateral view being obtusely angled after the basal 1/3 as opposed to strongly angled.
Females of Dineutus hornii can be somewhat fairly easily distinguished from those of D. assimilis and D. nigrior in that the apices of the elytra are angled towards the suture (Fig. 18A) as opposed to being rounded towards the produced sutural angle. This character combined with the epipleural color and the antennal flagellum shape should readily distinguish females of D. hornii from both D. assimilis and D. nigrior. Distribution (Fig. 52B). Extreme southeastern Canada from Saskatchewan to Nova Scotia (Majka 2008;Majka and Kenner 2009;Roughley 1991) and the eastern half of the United States as far south as Texas and northern Florida (Epler 2010; Figure 19. Dineutus hornii. A aedeagus dorsal view B aedeagus ventral view C ♂ mesotarsal claws D aedeagus lateral view. Scale bar for C ≈ 0.10 mm all others ≈ 1 mm. Ferkinhoff and Gunderson 1983;Folkerts 1978;Hilsenhoff 1990;Malcolm 1971;Roberts 1895;Sanderson 1982;Whiteman and Sites 2003;Wood 1962).
Habitat. This species is primarily lentic and occasionally found in streams (Hilsenhoff 1990; Whiteman and Sites 2003). In Canada D. hornii inhabits boggy and semiboggy lakes (Morrissette 1979). In the Missouri Prairie Region, Whiteman and Sites (2003) record this species in ponds with Brasneia.
Discussion. The spelling of the specific epithet hornii is in some places spelled horni, but the discrepancy in spelling was clarified by Majka (2008), finding "horni" to be an incorrect subsequent spelling of hornii. The unambiguously correct spelling is Dineutus hornii (Majka, 2008).
Dineutus hornii forms rafts during the daytime consisting of hundreds to thousands of individuals, which may be composed of multiple species (Heinrich and Vogt 1980). At night some individuals disperse to forage, returning to larger rafts of beetles just before dawn, while others do not leave the larger rafts formed during the day (Heinrich and Vogt 1980), unlike the behavior observed by Fitzgerald (1987) for D. nigrior where the diurnal rafts of this species appeared to totally disperse by night. Heinrich and Vogt (1980) suggest that D. hornii is nocturnal as foraging behavior occurs at night, with the diurnal period spent quiescently in rafts. Brief life history is available in Istock (1966;1967).
The larva of D. hornii was included in a key to gyrinid larvae by Hatch (1927) and the structure of the egg has been describe by Baker and Wai (1987).

Dineutus longimanus (Olivier, 1791)
Differential diagnosis. This is a very unique Dineutus species, easily distinguished from all other New World Dineutus, by the elytral apices possessing a spine located between the sutural and apicolateral angles. Serrations and irregularities are also present, and the sutural angle is also produced into a short spine. The venter is usually more lightly colored from reddish to yellow.
Distribution and subspecies. This species is endemic to the Caribbean and represents a bit of a population genetics and Caribbean biogeography problem. The species is currently divided into four subspecies, with each island of the Greater Antilles having its own subpsieces, with the two most unique subspecies being found at opposite ends of the species distribution (Cuba and Puerto Rico). The two subspecies occupying the middle area of the range (Jamaica and the Dominican Republic) are less distinct and seem to form a gradient between the morphologies of the two subspecies at the opposite ends. The aedeagi of three of the subspecies are very similar with only that of D. l. portoricensis offering some significant differences. For these reasons we have decided to retain the classification proposed by Ochs (1924Ochs ( , 1926aOchs ( , 1938 in treating the four forms as subspecies. Future genetic work may shed some light on these issues. Dineutus longimanus can be distinguished from all other North American species of Dineutus in having the elytral apices spinose with serrations and irregularities present. The subspecies can be separated by the following key: Diagnosis. Male (Fig. 20C-D). Size: 11.4-12.9 mm. Body form regularly elongate oval; elytral apices spinose, with sutural angle produce to a spine, and a second parasutural spine, with thorn-like serrations and irregularities present apically and apicolaterally, apicolateral sinuation mostly absent, elytra with reticulation strong laterally and apically, producing a bronzy appearance, medial disc with reticulation more weakly impressed and composed of smaller cells accompanied by very shallowly impressed punctation, striae mostly effaced by reticulation, if evident at all faintly apparent medially on disc, lateral marginal depression of elytra absent; profemora with very small sub-apicoventral tooth; protibiae club-shaped; mesotarsal claws ( Fig. 21C) with ventral margin regularly rounded and evenly narrowed apically; metacoxae with numerous shallow punctures present over most their ventral face; venter lighter in color: reddish brown to reddish orange. Aedeagus (Fig. 21A, B, D) with median lobe in dorsal view shorter than parameres, nearly parallel sided, slightly wider basally and shallowly narrowed apicad, in apical 1/4 shallowly narrowed towards apex, apex regularly rounded, dorsally without narrow carina, ventrally sperm-groove narrow and parallel sided for most its length, apically briefly widened, in lateral view median lobe with dorsal margin shallowly sinuate in apical 1/3, apex broadly rounded; parameres in dorsal view with lateral margins not laterally expanded, parallel sided for most their length, and apically narrowly rounded. Female (Fig. 20A-B). Size: 10.8-12.4 mm. Body form regularly elongate oval; elytral apices spinose, with sutural angle produce to a spine, and a second parasutural spine, with thorn-like serrations and irregularities present apically and apicolaterally, apicolateral sinuation mostly absent, elytra with reticulation strong laterally and apically, producing a bronzy appearance, medial disc with reticulation more weakly impressed and composed of smaller cells accompanied by very shallowly impressed punctation, striae mostly effaced by reticulation, if evident at all located medially on disc, lateral marginal depression of elytra absent; profemora without sub-apicoventral tooth; protibiae club-shaped; metacoxae with numerous shallow punctures present over most their ventral face; venter lighter in color: reddish brown to reddish orange. Differential diagnosis. Dineutus longimanus cubensis is unique among the other subspecies of D. longimanus in being smaller in size (10.8-12.9 mm) and having the metacoxae with numerous shallow punctures present and covering most of their surface. The subspecies most similar to D. l. cubensis is D. l. jamaicensis and can primarily be distinguished by the differences in dorsal punctation and the punctures of the metacoxae as provided by the indentification key. Distribution (Fig. 55B). Cuba (Leng and Mutchler 1914a;Ochs 1924Ochs , 1926 Habitat. Lotic, according to Peck et al. (1998) this subspecies occurs in streams through out Cuba and is an accidental cave inhabitant. Cave records for this species include Cueva Jíbara 8, Santiago de Cuba Province and Cueva Caja de Aqua, Saneti Spiritus Province (Peck et al. 1998).
Discussion. Information on the subspecies aside from its taxonomy has been scarce. Given what is currently known it appears that D. l. cubensis is only known from Cuba.
It is worth noting that the date of the description of D. l. cubensis is often given as 1926 (Ochs 1929(Ochs , 1938 as the name was used earlier by Ochs (1926Ochs ( -1927. However, according to Article 12.1 of The Code (ICZN 1999) in order for the nomen to be available it must be accompanied by a description or definition and in 1926 the name was simply used with an asterix making it a nomen nudum at that time. The description of D. l. cubensis was not included until the final part of the work published in 1927 on page 192 (Ochs 1927a). Thus the true date for D. l. cubensis must be 1927 as that is when the nomen satisfied the criteria of The Code for availability. Diagnosis. Male (Fig. 22C-D). Size: 12.1-13.3 mm. Body form regularly elongate oval; elytral apices spinose, with sutural angle produce to a spine, and a second parasutural spine, with thorn-like serrations and irregularities present apically and apicolaterally, apicolateral sinuation mostly absent, elytra with reticulation strong laterally and apically, producing a bronzy appearance, medial disc with reticulation very weakly impressed and composed of smaller irregularly more transversely shaped cells accompanied by very shallowly impressed punctation, striae mostly effaced by reticulation, if evident at all faintly apparent medially on disc, lateral marginal depression of elytra absent; profemora with very small sub-apicoventral tooth; protibiae club-shaped; mesotarsal claws ( Fig. 23C) with ventral margin regularly rounded and evenly narrowed apically; metacoxae with a decent covering of shallow punctures over most their ventral face, laterally only present on posterior half; venter lightly colored: reddish brown to reddish orange. Aedeagus (Figs 23A, B, D) with median lobe in dorsal view shorter than parameres, parallel sided, in apical 1/4 shallowly narrowed towards apex, apex regularly rounded, dorsally without narrow carina, ventrally sperm-groove narrow and parallel sided for most its length, apically briefly widened, in lateral view median lobe with dorsal margin straight, apex broadly rounded; parameres in dorsal view with lateral margins not noticeably laterally expanded, but very weakly sinuate medially, apically narrowly rounded.

Dineutus longimanus jamaicensis
Female (Fig. 22A-B). Size: 12.05 mm. Body form regularly elongate oval; elytral apices spinose, with sutural angle produce to a spine, and a second parasutural spine, with thorn-like serrations and irregularities present apically and apicolaterally, apicolateral sinuation mostly absent, elytra with reticulation strong laterally and apically, producing a bronzy appearance, medial disc with reticulation very weakly impressed and composed of smaller irregularly more transversely shaped cells accompanied by very shallowly impressed punctation, striae mostly effaced by reticulation, if evident at all faintly apparent medially on disc, lateral marginal depression of elytra absent; protibiae club-shaped; profemora without sub-apicoventral tooth; metacoxae with a decent covering of shallow punctures over most their ventral face, laterally only present on posterior half; venter lightly colored: reddish brown to reddish orange. Differential diagnosis. Dineutus longimanus jamaicensis is unique among the other subspecies of D. longimanus in being larger in size (12.05-13.3 mm) and elongate oval in shape without apicolateral sinuation, and having the metacoxae with numerous shallow punctures covering most of their surface. The subspecies most similar to D. l. jamaicensis is D. l. cubensis and can be distinguished by the differences in dorsal punctation and metacoxal punctation provided in the key. Distribution (Fig. 55B). Jamaica (Leng and Mutchler 1914b;Ochs 1938) Habitat. Specimen label data indicate this is a lotic subspecies, with specimens collected from the Mammee river in St. Andrew, Jamaica (FSCA).

Dineutus longimanus longimanus (Olivier, 1795)
Diagnosis. Male (Fig. 24C-D). Size: 12.3-13.9 mm. Body form regularly elongate oval, elytra laterally slightly broadened after basal half; elytral apices spinose, with sutural angle produce to a spine, and a second parasutural spine, with small thorn-like serrations and irregularities present apically but greatly reduced apicolaterally, apicolateral sinuation present and shallow, elytra with reticulation strong laterally and apically, producing a bronzy appearance, medial disc with reticulation more weakly impressed and composed of smaller transversely ovoid cells accompanied by shallowly impressed punctation, striae mostly effaced by reticulation, if evident at all faintly apparent medially on disc, lateral marginal depression of elytra shallow; profemora with very small sub-apicoventral tooth; protibiae club-shaped; mesotarsal claws ( Fig. 25C) with ventral margin with a well developed denticle; metacoxae with a sparse covering of very shallow punctures over most their ventral face, laterally only present on posterior margin; venter lightly colored: reddish orange to orangey yellow. Aedeagus (Fig. 25A, B, D) with median lobe in dorsal view shorter than parameres, nearly parallel sided, broader basally and weakly narrowed apicad, in apical 1/4 shallowly narrowed towards apex, apex regularly rounded, dorsally without narrow carina, ventrally sperm-groove narrow and parallel sided, in lateral view median lobe with dorsal margin straight, apex angularly rounded; parameres in dorsal view with lateral margins very weakly laterally expanded in apical 1/2, apically broadly rounded. Female (Fig. 24A-B). Size: 12.3-13.7 mm. Body form regularly elongate oval; elytral apices spinose, with sutural angle produce to a spine, and a second parasutural spine, with small thorn-like serrations and irregularities present apically but greatly reduced apicolaterally, apicolateral sinuation present and shallow, elytra with reticulation strong laterally and apically, producing a bronzy appearance, medial disc with reticulation more weakly impressed and composed of smaller transversely ovoid cells accompanied by very shallowly impressed punctation, striae mostly effaced by reticulation, if evident at all faintly apparent medially on disc, lateral marginal depression of elytra absent; protibiae club-shaped; profemora without sub-apicoventral tooth; metacoxae with a sparse covering of very shallow punctures over most their ventral face, laterally only present on posterior margin; venter lightly colored: reddish orange to orangey yellow.
Differential diagnosis. Dineutus longimanus longimanus is unique among other subspecies of Dineutus longimanus in being elongate oval and broadened posteriorly in the male after basal half of elytra, and having the metacoxae with sparse but present punctation. The subspecies most similar to D. l. longimanus is D. l. portoricensis but can be distinguished from D. l. portoricensis in being smaller in size (12.3-13.9 mm) and the aedeagus lacking a dorsal carina. Distribution (Fig. 55B). Haiti, Dominican Republic, (Leng and Mutchler 1914a;Ochs 1938;Wood 1962) Habitat. Lotic species collected in streams throughout the Dominican Republic (M. Fikáček pers. comm.).
Discussion. Similar to other species not much is known about this species aside from its taxonomy. The extant of range of this and other subspecies of D. longimanus may be obscured due to imprecise identification of subspecies.
Type designation. Olivier (1795) in his original description of G. longimanus states it is found in St. Domingue and was described from the cabinet of M. Bosc. A single specimen in the MNHN general collection has a label indicating both the aforementioned locality and being from Bosc's collection, as well as a label in the handwriting of Olivier with the I.D. of G. longimanus, therefore this specimen (Fig. 51E)  Diagnosis. Male (Fig. 26C-D). Size: 12.3-14.5 mm. Body form regularly elongate oval, elytra laterally slightly broadened after basal half; elytral apices spinose, with sutural angle produce to a spine, and a second parasutural spine, with small thorn-like serrations and irregularities present apically but greatly reduced apicolaterally, apicolateral sinuation present and shallow, elytra with reticulation strong laterally and apically, producing a bronzy appearance, medial disc with reticulation more weakly impressed and composed of smaller transversely ovoid cells along with very shallow punctation, striae mostly effaced by reticulation, if evident at all faintly apparent medially on disc, lateral marginal depression of elytra present and accompanied with a green sheen; profemora with very small sub-apicoventral tooth; protibiae club-shaped; mesotarsal claws ( Fig. 27C) with ventral margin with a weak denticle; metacoxae with a sparse covering of very shallow punctures that are almost indistinguishable over most their ventral face, laterally only present on posterior margin; venter lightly colored: reddish orange to yellow-orange. Aedeagus (Fig. 27A, B, D) with median lobe in dorsal view just shorter than parameres, broadest basally, becoming narrowed apicad after basal 1/3, then angularly narrowed again in apical 1/3 toward apex, apex narrowly rounded, dorsally with narrow carina, ventrally sperm-groove narrow and parallel sided, in lateral view median lobe with dorsal margin straight, slightly angled ventrally toward apex, apex broadly rounded; parameres in dorsal view with lateral margins not noticeably laterally expanded, apically broadly rounded. Female (Fig. 26A-B). Size: 11.2-13.4 mm. Body form regularly elongate oval; elytral apices spinose, with sutural angle produce to a spine, and a second parasutural spine, with small thorn-like serrations and irregularities present apically but greatly reduced apicolaterally, apicolateral sinuation present and shallow, elytra with reticulation strong laterally and apically, producing a bronzy appearance, medial disc with reticulation more weakly impressed and composed of smaller transversely ovoid sculpticells along with very shallowly impressed punctation, striae mostly effaced by reticulation, if evident at all faintly apparent medially on disc, lateral marginal depression of elytra present and accompanied with a green sheen; profemora without sub-apicoventral tooth; protibiae club-shaped; metacoxae with a sparse covering of very shallow punctures that are almost indistinguishable over most their ventral face, laterally only present on posterior margin; venter lightly colored: reddish orange to yellow-orange.
Differential diagnosis. Dineutus longimanus portoricensis can easily be distinguished from other subspecies of D. longimanus in being large in size (11.2-14.5 mm), elytral margin with a lateral green sheen, and most distinctly in the form of the aedeagus. The species most similar to D. l. portoricensis is D. l. longimanus but can easily be distinguished from it in being larger in size with the lateral marginal depression having a green sheen, and having the aedeagus with a dorsal carina. Distribution (Fig. 55B). Puerto Rico (Leng and Mutchler 1914b;Ochs 1924).
Habitat. Few specimens included habitat information. One that did, mentions a roadside stream (WIBF). Historical records also indicate this is a lotic subspecies (Ochs 1924).

Dineutus mexicanus
Differential diagnosis. Dineutus mexicanus is unique among all other North American Dineutus in having truncate elytra, with the lateral angle distinct, apicolateral sinuation weakly present, blunt serrations and irregularities present apically, males with a small acute profemoral sub-apicoventral tooth, and in the form of the aedeagus (Fig. 29A). The species most similar to D. mexicanus is D. truncatus (of which it used to be considered a subspecies of). The elytral truncature of D. mexicanus differs in form having the apicolateral margin of the eyltra weakly sinuate, the lateral angle distinct, and the striae being more evident than those of D. truncatus, especially in the males. There are also differences in body form discussed in the differential diagnosis section of D. truncatus.
Males of Dineutus mexicanus can further be separated from D. truncatus by the form of the protarsi (Fig. 30A), the mesotarsal claw shape, and the form of the aedeagus. See the differential diagnosis under D. truncatus for details.
For females see the differential diagnosis section for D. truncatus. Distribution (Fig. 54D). From Mexico to El Salvador (Arce-Pérez and Roughley 1999; Ochs 1949). Habitat. Unknown. Most specimens observed for this study were old, collected during the late 1950's to the early 1970's containing only locality data and lacking habitat data. A single specimen from Guatamela was collected in 2010 with the habitat data given as "oak forest at light" (FSCA).
Discussion. The elevation of D. mexicanus to full species status was based on the noticeable and significant differences between the aedeagi of D. truncatus and D. mexicanus as well as the external characters discussed in the differential diagnosis section for D. truncatus. These external characters include the protarsi, mesotarsal claws, and the elytral truncature, all found to be reliable indicators of species boundaries in North American Dineutus. The holotype (Fig. 51F) has been examined for this study allowing the characters of D. mexicanus to be unambiguously known and the species status elevation to be embedded securely in accordance with differences found in the type.
The extent of the range of D. mexicanus is currently unclear, due to the unclear identity of historical D. truncatus records. For the current study the eastern most record of D. mexicanus is from the Mico Quemado mountains near Progresso, Yoro, Hondoras (KSEM). Régimbart (1882) mentions a variety of D. truncatus from Honduras, which Ochs (1949) now appears correct in that this record actually refers to D. mexicanus. Specimens of D. mexicanus for this study were also found in El Salvador, from several localities representing the southern-most confirmed record of D. mexicanus. The western-most records for D. mexicanus from this study are from Nayarit, Mexico, 8 miles southeast of San Blas. Confirmed specimens of D. mexicanus are recorded from numerous records between these east and west localities including Guatemala, and the Mexican states of Veracruz, Oaxaca, and Guerrero. It is unclear how far north the range of D. mexicanus extends in Central America and the Isthmus of Tehuanatepec. Based on the limited range data (Fig. 54D), it appears that D. mexicanus may be a mountain endemic, following the Sierra de Madre de Chiapas through Chiapas, Mexico, Guatemala, and into El Salvador and Honduras, going northwest to southeast through its range. Therefore, D. mexicanus may indeed be absent from the Northern Guatemala, Belize, and the Mexican states of Quintana Roo, Yucatan, Campeche, and Tabasco. In the west Dineutus mexicanus records again overlap with mountain ranges, being found in western Oaxaca in the Sierra Madre del Sur, going northwest along the western portion of the Trans-Mexican Volcanic Belt and into the Sierra Madre Occidental, as far north as Nayarit. Ochs (1949)   Diagnosis. Male (Fig. 31C-D): Size: 11.1-11.7 mm. Body form narrowly oval; elytral apices with sutural angle produced into a point, elytral striae faint basally becoming more evident apically and laterally; profemora without a sub-apicoventral tooth; protibiae wedge-shaped, with distolateral margin produced; mesotarsal claws markedly asymmetrical (Fig. 32C), anterior mesotarsal claw larger than posterior claw, venter darkly colored, reddish brown to black with mesothoracic and metathoracic legs lighter in color; Aedeagus (Fig. 32A, B, D) median lobe in dorsal view narrowed in api- cal 1/4, shortly rounded apically, in lateral view apex of median lobe strongly curved dorsally, parameres strongly curved in lateral view after basal 1/3. Female (Fig. 31A-B): Size: 11.6-11.7 mm. Body form narrowly oval; elytral apices produced and rounded, with sutural angle produced into a point, apicolateral sinuation strong, elytral striae faint basally, becoming more evident apically and laterally; profemora without sub-apicoventral tooth; protibiae laterally weakly curved, distolateral margin weakly expanded; venter darkly colored, reddish brown to black venter darkly colored, reddish brown to black with mesothoracic and metathoracic legs lighter in color.
Differential diagnosis. This species is unique among all other species of North American Dineutus in the extremely large size and assymetrical nature of the male mesotarsal claws (Fig. 32C) and the form of male aedeagus (Fig. 32A, B, D). The species most similar to Dineutus nigrior are Dineutus assimilis and Dineutus hornii, of the two the former most closely resembles D. nigrior especially the female members of the species. Females of all three species very closely resemble one another and require careful consideration for identification. Males of the species can be fairly readily distinguished externally, and aedeagal dissections can indisputably separate males of the species.
In general males of D. nigrior can be distinguished from members of D. assimilis and D. hornii by size. Dineutus nigrior males are larger (Size: 11.1-11.7 mm) than males of both D. assimilis and D. hornii. Dineutus nigrior males differ from males of D. hornii in having the sutural angle of the elytral apices produced into a point, and the venter of D. nigrior is much more darkly colored than that of D. hornii, with the epipleura being similarly colored as the thoracic ventrites. Males of D. nigrior can be distinguished from both D. assimilis and D. hornii in having the mesotarsal claws markedly asymmetrical (Fig. 32C) with the anterior tarsal claw being larger than the posterior claw, while in both D. assimilis (Fig. 9C) and in D. hornii (Fig. 19C) the mesotarsal claws are similar in size. The distolateral margin of the protibiae in D. nigrior is produced while in D. assimilis and D. hornii the margin is straight or nearly so. The aedeagus of D. nigrior (Fig. 32A) is most similar to D. hornii (Fig. 19A) but can be distinguished from D. hornii in having the apex of the median lobe strongly curved dorsally in lateral view (Fig. 32D).
The females of D. nigrior are also generally larger (Size: 11.6-11.7 mm) than those of D. assimilis and D. hornii, but unlike the case in the males, females of each of these three species have the sutural angles of the elytra produced into a point. However, the shape of the apices differs between them. In females of D. nigrior the apices of the elytra are regularly rounded, and this situation is most different from D. hornii where the apices are generally angled towards the sutural production. Dineutus nigrior females can be separated from both D. assimilis and from D. hornii in having the distolateral protibial margin produced, similar to the condition in males, but more weakly expanded. Distribution (Fig. 52C). Extreme southeastern Canada from Manitoba to Nova Scotia (Majka 2008;Majka and Kenner 2009;Roughley 1991) and most of the eastern half of the United States as far south as northern Florida (Epler 2010;Folkerts 1978;Gordon and Post 1965;Hilsenhoff 1990;Malcolm 1971;Régimbart 1907;Roberts 1895;Sanderson 1982;Whiteman and Sites 2003;Wood 1962).
Habitat. Primarily lentic species, found only infrequently in streams (Roberts 1895;Hilsenhoff 1990). In Canada, D. nigrior prefers semi-boggy lakes (Morrissette 1979). In the Missouri Prairie Region, Whiteman and Sites (2003) found this species associated with the plant taxa Brasneia and Lespedeza.
Discussion. Fitzgerald (1987) described the social system of Dineutus nigrior in detail and Fairn et al. (2008) studied the effects of parasitism by larval water mites of the genus Eylais Latreille, 1796 on adults of Dineutus nigrior. Evidence for sexual selection within this species has also been investigated (Fairn et al. 2007a;Fairn et al. 2007b). Brief life history information is available in Istock (1966;1967).
Key to the larvae of D. nigrior provided by Hatch (1927).  Diagnosis. Male (Fig. 33C, D): Size: 9.5-9.6 mm. Body form narrowly elongate oval; elytral apices rounded with sutural angle produced to a point, apicolateral sinuation weakly present, irregularities present apically near sutural production, elytral apices strongly deflexed, reticulation of pronotal and elytral discs strongly impressed, producing a bronzy appearance; elytral striae faintly evident, most evident on the subapicomedial portion of the elytral disc; profemora with a very small sub-apicoventral tooth, accompanied by a series of denticles extending proximad, associated with each posterior setigerous puncture of the profemora; protibiae subsinuate; mesotarsal claws ( Fig. 34C) long and of similar size, with ventral margin straight; venter darkly colored, usually black to very dark bronzy-brown, with the tibiae and tarsi of mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen; Aedeagus (Fig. 34A, B, D) median lobe in dorsal view noticeably shorter than parameres, weakly constricted just apicad to middle, acuminate in apical ca. 1/5, apex of acumination flatly rounded, in lateral view median lobe roundly curved dorsally, in dorsal view parameres sinuate laterally after basal 1/3, in apical 1/3 laterally expanded, apically strongly rounded. Female (Fig. 33A, B): Size: 9.5-9.9 mm. Body form narrowly elongate oval; elytral apices angled towards very strong sutural production, apicolateral sinuation strongly present and with plica, irregularities present apically near sutural production, elytral apices strongly deflexed, reticulation of pronotal and elytral discs strongly impressed, producing a bronzy appearance; elytral striae faintly evident, most evident on the subapicomedial portion of the elytral disc; profemora without sub-apicoventral tooth; protibiae club shaped, with lateral margin round, weakly expanded apicaly; venter darkly colored, usually black to very dark bronzy-brown, with the tibiae and tarsi of mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen.

Dineutus productus
Differential diagnosis. Dineutus productus can be distinguished from all other North American Dineutus in males having the profemora with a small sub-apicoventral tooth, accompanied by a series of denticles that extend proximad, with each denticle being associated with a posterior setigerous puncture of the profemora, elongate mesotarsal claws of equal size, with straight ventral margins (Fig. 34C), and in the form of the aedeagus (Fig. 34A). The species most similar to D. productus is D. serrulatus analis. The nominal subspecies of D. serrulatus serrulatus should not be confused with D. pro- ductus in that it has a restricted range in Florida, and its elytral apices would not easy be confused with those of D. productus, being regularly rounded, with a strong apicolateral sinuation in both sexes and the dorsum being polished black in appearance. Dineutus serrulatus analis on the other hand tends to be variable in the appearance of the elytra (Fig. 37A, C), with some members having the sutural angle produced and the dorsum with strong microreticulation giving the elytra and pronotum a polished bronzed appearance, similar in both respects to D. productus.
Dineutus productus can generally be separated from D. serrulatus analis in having a more elongate narrow body form (Fig. 33A, C), and being smaller in size. Dineutus productus is much more narrowly attenuated anteriorly, compared to D. s. analis, which is broader in body form and larger in size. The ventral coloration of D. productus is most often black to very dark brownish red, and frequently accompanied by a bronzy metallic sheen, while the venter of D. s. analis is most often red in color, rarely appearing black and often lacking any metallic sheen. When more darkly colored D. s. analis is much more red in hue, compared to when D. productus is more lightly colored, having a more brownish hue. A few specimens of D. s. analis examined from southeast Kansas had their venters truly black (KSEM) and for these specimens differences between the male secondary sexual characters as well as differences in the elytra allowed for unambiguous identification. The serration of the elytral apices differs between these two species. In D. productus the apices of the elytra only have irregularities present, at most having round bumps that resemble highly reduced serration, while in D. s. analis the serration is present as distinct and fine points.
The males of D. productus can easily be distinguished from those of D. s. analis in that the profemoral sub-apicoventral tooth is small and accompanied by a series of denticles that extend proximad, with each denticle being associated with a posterior setigerous puncture of the profemora, in D. s. analis there is a profemoral subapicoventral tooth as normal, but no accompanying series of denticles. This character appears unique to D. productus among all of the North American Dineutus species. The mesotarsal claws also differ greatly between these two species. Dineutus productus males have the mesotarsal claws elongate with their ventral margins straight (Fig. 34C) and lacking a denticle, while in D. s. analis the mesotarsal claws are small, with their ventral margins curved and possessing a denticle (38F). The aedeagus is by far the most definite way to separate the two species. The aedeagus of D. productus (Fig. 34A) has the median lobe shorter than the parameres, and strongly acuminate apically, with the parameres being sinuate after the basal 1/3 and laterally expanded in the apical 1/3, with the apices rounded. In D. s. analis the median lobe (Fig. 38A, D, H) is as long as the parameres, parallel sided for most its length, having only the apical 1/4 narrowed, with the parameres being parallel sided for most of their length, being only weakly expanded in the apical 1/3 and often obliquely truncate, or obliquely flatly rounded.
Females of D. productus (Fig. 33A) can be distinguished from those of D. s. analis in having a much greater apicolateral sinuation of the elytra, the sinuation is so deep that a plica is formed, and the elytral apices have a much steeper angle towards the sutural production than in D. s. analis females (Fig. 37A), which have a much more shallow apicolateral sinuation and more rounded elytral apices. As mentioned earlier the elytra of D. productus have irregularities present apically, but not fine serration, as seen in D. s. analis. Distribution (Fig. 54A). Central and south-central United States (Roberts 1895), into northeastern Mexico (Ochs 1949). As this species is so rarely collected, we list here the states and counties where it has been collected and the identification is not in question: USA: Kansas: Bourbon Co., Elk Co, Greenwood Co., Lyon Co., Morris Co. (this study) (Wood 1962); Mexico: Nuevo Leon: Granja Rodriguez on the borders of the Rio Salado alt. 195m (Ochs 1949).
Habitat. Lotic species, the Kansas Biological Survey field notes (available at the KSEM) indicate the species was collected from slow moving, cool, mud bottomed streams, that were fairly wide. Gustafson et al. (2014) describe the habitat where D. productus was recently collected in detail, accompanied by photos of the habitats. The species has also been taken at light traps placed at water level in the vicinity of rapids, on the borders of the Rio Salado, in Nuevo Leon, Mexico (Ochs 1949).
Discussion. Dineutus productus appears to be an uncommonly collected species and the reason for this is not exactly clear. Most species found in the United States are uncommon due to a narrow range of endemism (e.g. D. robertsi and D. angustus), but material examined in this study, as well as records from the literature, suggest the range of this species is not as narrow as the previously mentioned species. Dineutus productus was originally described from Texas by Roberts (1895), and most records of this species come from this state (Régimbart 1907;Ochs 1929;Wood 1962). Young (1954) claimed to have specimens from the panhandle of Florida, but Epler (2010) re-examined specimens in the FSCA identified by Young as D. productus, finding them to belong to other species. Hatch (1925a) claimed to have collected the species from the Sangamon River near Decatur, Illinois. Ochs (1949) however, questioned the Illinois record as well as Régimbart's (1907) from the Carolinas, stating all specimens identified as D. productus from outside of Texas actually belonged to other species upon his examination. In the same paper Ochs (1949) extended the species range southward in to Neuvo Leon, Mexico.
Material examined for this study from Kansas (KSEM, GTGC), was undoubtedly Dineutus productus, confirming that the range of D. productus extends at least that far northward. This adds credence to Hatch's (1925a) record from Illinois. Furthermore, comparing images of the Sangamon River available online to those provided by Gustafson et al. (2014), they appear to be the same habitat. The first author was unable to locate Régimbart's specimen of D. productus within the MNHN, in order to confirm Régimbart's 1907 record, but D. productus was not listed as a species of Dineutus found in North and South Carolina by Sanderson (1982). Given this and the inability to locate the specimen of Régimbart's from the Carolinas in his collection at the MNHN, we do not treat Régimbart's 1907 record as a part of the species range. Ochs' diagnosis of D. productus (1949) matchs our own, therefore we accept his record for the species from Nuevo Leon, Mexico as representing the southern-most extreme for the range. As mentioned above, given the new Kansas records for the species and the habitat photos of the Sangamon River available online, we accept Hatch's (1925a) record from Illinois, as the northern-most extreme for the species' range.

Specimens examined. 59
Type material examined. Not examined, but specimens collected from the type locality.
Differential diagnosis. This species is easily distinguished from all other North American species of Dineutus by its large size, profemora lacking a sub-apicoventral tooth, entirely bronzy elytra, and broadly oval body shape with a pale yellow venter. Other North American species with pale venters are much more attenuated in body shape (e.g. Dineutus discolor, Dineutus longimanus).
The species most similar to Dineutus robertsi is D. ciliatus. Dineutus robertsi differs from D. ciliatus in having the antennal club narrow and parallel sided, with the ultimate segment elongate and pointed apically, as opposed to having the flagellum being thicker and rounder with the ultimate segment rounded. Dineutus robertsi also has the 8 th elytral stria with punctures evident laterally as opposed to having them absent or indistinct as in D. ciliatus. The males of D. robertsi can further be distinguished from D. ciliatus in having the anterior mesotarsal claw (Fig. 36C) with a strong denticle. The aedeagus of D. robertsi (Fig. 36A) has the median lobe in dorsal view flatly rounded apically with the apex lacking an apicomedial papilla, as compared to D. ciliatus (Fig. 13A) in which an apicomedial papilla is present. In ventral view (Fig. 36B), the sperm-groove of the median lob is triangular, narrowed posteriorly and anteriorly, as opposed to that of D. ciliatus (13B) which is broader and more parallel sided. In lateral view the median lobe of D. robertsi (Fig. 36D) is thick and flat, not dorsally curved as is the case in D. ciliatus (Fig. 13D). The parameres also differ in being strongly arced in apical 1/3, those of D. ciliatus are weakly arced. Distribution (Fig. 53B). Known from the Appalachian mountains of northeastern Georgia, and southwestern North and South Carolina in the United States (Leng 1911;Sanderson 1982;Wood 1962).
Habitat. Lotic species, frequenting mountainous streams with rocky bottoms. The second author collected many specimens from moderately high gradient, rocky streams in higher elevation mountainous regions in the southern Appalachians. Specimens were common in pools and margins of the streams. They were not found at lower elevations or on larger rivers where they were replaced by D. discolor and D. ciliatus.
Discussion. Dineutus robertsi is highly endemic to the Appalachians of northeastern Georgia and southwestertn North and South Carolina (Fig. 53B). For this reason D. robertsi has been infrequently collected and is poorly represented in collections. Once in the range of this species however, it can be regularly collected on mountain streams, and in large numbers. The full extent of the range of D. robertsi is still in question. Further sampling of the Appalachians would be greatly beneficial for determining the extent of the range of this highly endemic species.

Dineutus serrulatus LeConte, 1868
Differential diagnosis. Overall this species can be diagnosed in having elytral apices that are serrulate and with apicolateral sinuation present in both sexes, red colored venters, males with a profemoral sub-apicoventral tooth, and in the form of the male aedeagus. A key to the subspecies is provided and each subspecies is treated individually. Distribution and subspecies. This species is wide-ranging, highly variable among populations (Fig. 39), and has been divided into two subspecies: D. serrulatus serrulatus and D. s. analis (Wood 1968). Of these subspecies D. serrulatus serrulatus is more consistent in its characters, while those of D. s. analis are much more variable causing difficulties in separating the two. Dineutus serrulatus analis was originally described as a separate species by Régimbart in 1882, but was relegated to a subspecies of D. serrulatus LeConte by Wood (1968). Recent papers have again treated D. analis as a separate valid species (e.g. Ciegler et al 2003;Realzola et al. 2007). For this study the authors found no single discrete character that could reliably separate the taxa. Although dorsal coloration can usually be used to separate the two subspecies, populations from northern Florida where the two subspecies meet, show intermediate dorsal coloration, being medially polished black, but laterally bronzy green. Furthermore the aedeagi, of the two subspecies are very similar, with only minor differences that appear variable across the entire range of this species. Another useful character for delimiting similar species, the mesotarsal claws, are also similar showing only minor variation. For these reasons we continue to follow Wood (1968) in treating these two taxa as subspecies.
Diagnosis. Male (Fig. 37C-D): Size: 9.9-11.4 mm. Body form elongate oval; elytral apices flatly rounded, often with sutural angle produced to a point, apicolateral sinuation present, with sinuation shallow, serration and irregularities present apically near sutural production, elytral apices weakly deflexed, reticulation of pronotal and  elytral discs strongly impressed, producing a bronzy appearance; elytral striae faintly evident, most evident on the medial portion of the elytral disc; profemora with subapicoventral tooth; protibiae subsinuate; mesotarsal claws ( Fig. 38F) small and of similar size, with ventral margin with a more or less developed smooth denticle; venter lightly or darkly colored, coloration usually red but ranging to very dark red or black, with the mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen; Aedeagus ( Fig. 38A-C, D, E, G, H-J) with median lobe in dorsal view as long as parameres, highly parallel sided, narrowed in apical 1/4, apex flatly to regularly rounded, in lateral view median lobe weakly curved dorsally after basal 1/3, parameres in apical 1/3 weakly laterally expanded, apically obliquely flatly rounded to truncate.
Female (Fig. 37A-B): Size: 10.0-11.4 mm. Body form elongate oval; elytral apices flatly rounded, sutural angle often produced to a point, apicolateral sinuation shallow, serration present apically near sutural production, elytral apices weakly deflexed, reticulation of pronotal and elytral discs strongly impressed, producing a bronzy appearance; elytral striae faintly evident, most evident on the medial portion of the elytral disc; profemora without sub-apicoventral tooth; protibiae club shaped, with lateral margin flatly round; venter lightly or darkly colored, coloration usually red but ranging to very dark red or black, with the mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen.
Differential diagnosis. Dineutus serrulatus analis is unique among all other North American Dineutus species in belong elongate oval and attenuated anteriorly, with elytral apices having apicolateral sinuations in both sexes, flatly rounded elytral apices, often with the sutural angle produced to a point, and with serration present, males with the profemora with a sub-apicoventral tooth, and in the form of the male aedeagus. The species most similar to D. s. analis is D. productus. Dineutus s. analis can be separated from D. productus by the differential diagnosis given for D. productus.
Habitat. Lotic species found in small streams usually below 500 feet in elevation (Wood 1968). For a more in depth description of habitat see (Gustafson et al. 2014).
Discussion. Of the two subspecies D. s. analis has the wider of the two ranges (Wood 1968). Dineutus s. serrulatus is primarily distributed in Florida and to the east in the Carolinas (Young 1954;Sanderson 1982). In northern Florida where the two subspecies meet specimens show intermediate morphology. Specimens examined in this study from Liberty County, Florida, (Fig. 39D [FSCA]) showed intermediate dorsal coloration being polished black medially, but laterally bronzy green and the sperm-groove of the aedeagus (Fig. 38B) is intermediate between the narrowed sperm-groove of northern populations of D. s. analis and the more broad sperm-groove of D. s. serrulatus from southern Florida. These specimens from Liberty County (FSCA) also show unique variation in the parameres (Fig. 38A), in that they are much more narrow and parallel sided in their apical half, not exhibiting the lateral expansions and arc seen in the parameres of other populations. However, the median lobe is identical in shape to that of D. s. serrulatus. While this variation in the past may have been enough to qualify as sub-specific differences, given how highly variable this species is (Fig. 39), no formal name will be applied at this time. Making the situation even more difficult, D. s. analis from Texas (Fig. 38D, E [KSEM]) have the aedeagus and sperm-groove identical to those of D. s. serrulatus (Fig. 41A, B). Specimens from southeastern Kansas (KSEM) were notable for having a bronzy dorsal surface, but a very dark reddish brown venter (Fig. 39J, K). The profemoral subapicoventral tooth is also quite large for a member of D. s. analis. Future genetic work may shed better light on the significance of this variation.
Type designation. Régimbart (1882) in the original description describes the species from both Louisiana and Texas. In the MNHN there are two specimens from the Régimbart Collection, one from Texas and one from Louisiana. Here we formerly designate the specimen from Texas (Fig. 51A)  Diagnosis. Male (Fig. 40C-D): Size: 9.9-11.7 mm. Body form broadly elongate oval; elytral apices flatly rounded, rarely with sutural angle produced to a point, apicolateral sinuation strongly present, serration and irregularities present apically near sutural production, elytral apices weakly deflexed, reticulation of pronotal fine, producing a polished appearance; elytral striae faintly evident, most evident on the medial portion of the elytral disc; profemora with large sub-apicoventral tooth; protibiae subsinuate to weakly-subsinuate; mesotarsal claws ( Fig. 41C) small and of similar size, with ventral margin with a more less developed smooth denticle; venter lightly colored, red in coloration for its entirety, with the mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen; Aedeagus (Fig. 41A, B, D) with median lobe in dorsal view as long as parameres, highly parallel sided, narrowed in apical 1/4, apex flatly to regularly rounded, in lateral view median lobe weakly curved dorsally after basal 1/3, in ventral view sperm-groove broad, parameres in apical 1/3 weakly laterally expanded, apically obliquely flatly rounded to truncate. Female ( Fig. 40A-B): Size: 9.6-11.3 mm. Body form elongate oval; elytral apices flatly rounded to flatly rounded toward apical production, sutural angle often produced to a point, apicolateral sinuation shallow, serration present apically near sutural production, elytral apices weakly deflexed, reticulation of pronotal fine, producing a polished appearance; elytral striae faintly evident, most evident on the medial portion of the elytral disc, profemora without sub-apicoventral tooth; protibiae club shaped, with lateral margin flatly round; venter lightly colored, red in coloration for its entirety, with the mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen.
Differential diagnosis. Dineutus serrulatus serrulatus is unique among all other North American Dineutus in being elongate oval and attenuated anteriorly, having the elytral apices flatly rounded with serration present apically near the suture, both sexes with apicolateral sinuation present, being deeply sinuate in the males, males with a large and highly acute sub-apicoventral profemoral tooth, and in the form of the aedeagus. The species most similar to D. s. serrulatus is D. carolinus. Both D. s. serrulatus and D. carolinus have the elytral apices with serrations and or irregularities present apically. Dineutus s. serrulatus of both sexes can be distinguished fairly easily from D. carolinus in the color of the venter. The venter of D. s. serrulatus is more lightly colored (Fig. 40B, D), varying from light orange red to a dark orange red, while that of D. carolinus is darkly colored, dark reddish brown to black (Fig. 10B, D). The body form between the two species also differs in D. s. serrulatus is more attenuated anteriorly, while D. carolinus is more regularly elongate oval in body form Males of D. s. serrulatus can be further distinguished from D. carolinus in having a strong apicolateral sinuation present in the elytra. Males of D. carolinus do not have apicolateral sinuation present. The profemoral sub-apicoventral tooth will also separate the species in that D. s. serrulatus has a very large acute tooth, while that of D. carolinus is much smaller. The mesotarsal claws are also very different between these two species, in D. s. serrulatus the ventral margin has a denticle (Fig. 41C), while in D. carolinus the ventral-margins are shallowly rounded and without a denticle (Fig. 11C). The male aedeagus will allow unambiguous separation of the two species. In D. s. serrulatus the median lobe of the aedeagus (Fig. 41A) is highly parallel sided, being only narrowed in the apical 1/4 while D. carolinus the aedeagus is gradually tapered from base to apex (Fig. 11A). The parameres differ drastically between the species. In D. s. serrulatus the parameres are much more narrow and are obliquely truncate to obliquely flatly rounded, while in D. carolinus the parameres are thick and broad and are apically flatly rounded, not obliquely angled. Females of D. s. serrulatus are more difficult to distinguish from females of D. carolinus as both have an apicolateral sinuation present in the elytra. But the venter coloration and body form differences should allow separation of these two species.
Habitat. Dineutus serrulatus serrulatus is a lotic species (Young 1954;Wood 1968) and appears to occupy small streams below 500 feet in elevation (Wood 1968). In Florida D. s. serrulatus is commonly found in small, rather swift, sand bottomed streams of the uplands throughout the northern and central peninsular region, as well as in the western uplands (Young 1954). Young (1954) suggests that D. s. serrulatus is more rarely found in the swifter streams of the flatwoods. Young (1954) also notes that D. s. serrulatus is rarely found in the same habitat as D. angustus in the peninsular uplands of Florida, and attributes this to D. s. serrulatus being found in slightly more acidic streams.
Discussion. It should be pointed out that D. s. serrulatus has the more narrower of the two subspecies ranges, occupying the most southeastern portion of the species range (Fig. 53C).  subsinuate to club-shaped; mesotarsal claws ( Fig. 43C) with ventral margin straight, with weak medial expansion; venter darkly colored, usually black to very dark reddish brown, mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen; Aedeagus (Fig. 43A, B, D) median lobe in dorsal view just shorter than parameres, mildly parallel sided, weakly angled towards apex, acuminate in apical 1/5, apical median lobe angled towards acumination, lateral margins of acumination angled toward apex, apex very shortly rounded producing a strong point, in lateral view median lobe evenly shallowly curved dorsally, ventrally median lobe with diamond shaped sperm-groove, parameres in dorsal view weakly expanded laterally at apical 1/3, narrowly rounded apically.

Dineutus solitarius
Female (Fig. 42A-B): Size: 9.1-10.2 mm. Body form regularly oval; elytral apices regularly broadly rounded, with serrations and irregularities absent apically, apicolateral sinuation absent, elytra reticulation course and well impressed laterally, medially being replaced by fine microreticulation, elytral disc medially often with fine and weakly impressed punctures, striae very faintly present, most evident medially on elytral disc; profemora without sub-apicoventral tooth; protibiae club-shaped; venter darkly colored, usually black to very dark brown, mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen.
Differential diagnosis. Dineutus solitarius is unique among all other North American Dineutus in being smaller in size (9.1-10.4 mm), with a broadly oval body form (Fig. 42C), having the elytral apices broadly rounded without serrations and/or irregularities, males with the profemoral sub-apical ventral tooth small and atop a carina, and by the form of the aedeagus (Fig. 43A). The species most similar to D. solitarius are D. carolinus and D. emarginatus. Both sexes of D. solitarius can be distinguished from D. carolinus in having the elytral apices broadly rounded without apical serrations and/or irregularities, as opposed to having the elytral apices narrowly rounded with serrations and/or irregularities present. The body form of D. solitarius is much more regularly oval as opposed to being more elongate overall in D. carolinus. Dineutus solitarius lacks a defined lateral marginal depression as seen in D. carolinus as a result of being more dorsoventrally convex.
Of the two species similar to D. solitarius, D. emarginatus is more similar, in that both of these species have the elytral apices fairly broadly rounded and without apical serrations and/or irregularities present. Furthermore, the aedeagi of these two species are somewhat similar both being acuminate. In general both sexes of D. solitarius can be distinguished from D. emarginatus in being much more regularly rounded in body form than D. emarginatus, whose body form is more elongate oval. The pronotal shape of the two species differs fairly noticeably, in D. solitarius the pronotum has the lateral borders much more obtusely angled posteriorly to anteriorly, and the posterior margin of the pronotum flatly meets the posterolateral corners of the pronotum, while in D. emarginatus the pronotum has the lateral borders more straightly angled posteriorly to anteriorly with the posterior margin being more sinuate.
Males of D. solitarius can further be removed from D. emarginatus in having a small profemoral sub-apicoventral tooth atop a carina, while in D. emarginatus the tooth is much more large and triangular. The aedeagi of these two species are similar in that both have an acuminate median lobe, however the general shape of the median lobe of the two aedeagi can be separated without difficulty. The median lob of D. solitarius (Fig. 43A) is much more parallel sided, being weakly narrowed towards the acumination and the acumination itself having its margins angled towards the apex, which is very narrowly rounded giving it a very pointed feel. In D. emarginatus the median lobe (Fig. 20A) is weakly constricted medially giving the lateral margins a slight sinuation, the apical margins of the median lobe are rounded towards the acumination, with the acumination having its lateral margins fairly straight, and the apex relatively more broadly rounded, giving it a more rounded pointed shape, as opposed to narrowly pointed as in D. solitarius.
The females of D. solitarius differ primarily in the general differences between the two species. Distribution (Fig. 54B). From extreme southern United States, Texas ("Pinto Texas" 1938 [KSEM]) and California (Leech 1940;Leech 1948), throughout Mexico (Ochs 1949) and Central America to western Costa Rica. The first author visited the only known California locality, the city of Mecca, in Riverside County, in southwestern California, in the summer of 2012, in an attempt to recollect this species. The area had changed quite a bit with much of the duck ponds in the area having dried up and an increased agricultural presence was evident.
Habitat. This species appears to be lotic. Several locality labels list "pools in stream". In La Selva Negra, Nicaragua, specimens were collected from a pool within a stream by the second author.

Discussion.
It should be noted that D. solitarius is primarily a Mexican and Central American species, only just barely reaching the United States. Historical records indicate it was at one point found in California (Leech 1940) and Texas.
There is some noticeable variation in the elytral sculpturing among populations of D. solitarius. Specimens from Sierra de Zapotan, Nayarit, Mexico (UCRC) have the punctures of the elytra much more shallowly and weakly impressed, making them much larger and "dimply" in appearance (Fig. 46B). This is most noticeable medially on the elytra discs near the sutural region, where the strong lateral reticulation is replaced by the fine mesh microreticulation. Interestingly a similar situation is seen in specimens from the same area of Dineutus sublineatus (Fig. 46A). These specimens with the dimply punctation make it apparent that the fine weakly impressed punctation seen normally medially on the elytral discs is also present laterally, but is obscured by the strong reticulation of that area, and is visible medially and suturally due to the fine microreticulation of that area. Specimens from Costa Rica (MSBA) also show variation in elytral sculpturing, having the reticulation of the elytra composed of much finer meshes. The lateral meshes are still stronger but not nearly as coarse as in other populations. Specimens of D. solitarius from Oaxaca, Mexico, near Arriba, (FSCA) show variation in body form. The outline of the body is much more broadly oval in these specimens. There is also a much greater dorsoventral convexity in the scutellar region, especially evident in lateral view. It should be noted that although there are these variations among populations, the aedeagi of males from each of these populations are not noticeably different or variable in any significant manner.
Type designation. Similar to the situation with D. metallicus Aubé, the only specimen with a date and Aubé's handwriting for the determination label was selected as the lectotype (Fig. 51C). The other specimens in the MNHN collection lacked dates and/ or Aubé's handwriting, therefore we did not designate paralectotypes. Diagnosis. Male (Fig. 44C-D): Size: 12.3-15.5 mm. Body form elongate broadly oval; elytral apices broadly or flatly rounded/subtruncate, with serrations and irregularities absent apically, apicolateral sinuation weakly present, each elytron with all 9 elytral striae well developed, elytral stria 1 and 2 often obscured suturally and near the scutellar region by dense microreticulation, often accompanied by fine weakly impressed punctures; profemora with highly acute sub-apicoventral tooth; protibiae club-shaped; mesotarsal claws similar in size with very weak denticle (Fig. 45C) venter darkly colored, usually black to dark reddish brown, mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen; Aedeagus (Fig. 45A, B, D) median lobe in dorsal view nearly as long as parameres, narrow, becoming attenuated apically, apex very narrowly rounded, in lateral view median lobe becoming highly narrowed ventrally in apical 1/3, shallowly curved dorsally after basal 1/3, ventrally median lobe with parallel sided sperm-groove, parameres in dorsal view very weakly expanded laterally at apical 1/3, angled apically. Female (Fig. 44A-B): Size: 12.6-14.0 mm. Body form regularly oval; elytral apices broadly or flatly rounded/subtruncate, with serrations and irregularities absent apically, apicolateral sinuation usually weakly present, each elytron with all 9 elytral striae well developed, elytral stria 1 and 2 often obscured suturally and near the scutellar region by dense microreticulation, often accompanied by fine weakly impressed punctures; profemora without sub-apicoventral tooth; protibiae club-shaped; venter darkly colored, usually black to very dark brown, mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen, abdominal sternite VII with medial expansion of posterior margin. Differential diagnosis. Dineutus sublineatus is unique among all North American Dineutus in being large in size, with a more or less regularly elongate oval body form, with all 9 elytral striae strongly evident, males with a small well developed and highly acute profemoral sub-apicoventral tooth, the form of the aedeagus (Fig. 45A), and females with abdominal sternite VII (Fig. 44B) with a medial expansion of the posterior margin. This species is highly unique in having the elytral striae well developed and highly evident. All other species have the elytral striae primarily faintly evident, or apparent but not strongly developed. All 9 elytral striae are evident, and often for most their length. Striae 1 and 2 can be obscured near the scutellar region as well as the near the sutural region of the elytra, by the microreticulation of these areas, which is often accompanied by fine weakly impressed punctures. An even more unique character of this species is the medial expansion of the posterior margin of abdominal sternite VII in the female. This is unique among the females of all Ne World Dinuetus. This species is similar to other Mexican and Central American species in coloration, being dorsally olive green with light violet reflections laterally on the elytra, and with the venter being very darkly colored black to reddish brown. However, D. sublineatus unlike the other large Mexican and Central American species has the elytral apices regularly to flatly rounded/subtruncate, as opposed to being truly truncate. Distribution (Fig. 54C). Extreme southwestern U.S., throughout most of Mexico and central Central America to Nicaragua (Blackwelder 1944;Leech 1948;Ochs 1949;Régimbart 1882;1907;Roberts 1895;Wood 1962).
Habitat. Lotic and lentic. In Oaxaca, Mexico, 43 mi w of Tehuantepec D. sublineatus was collected in pools in mountain streams at 2500-3000 ft in elevation (FSCA). Other label data also indicate pools in steams. In the United States the second author has collected this species in pools in dry streambeds within canyons in southern Arizona.
Discussion. There is dimorphism in body form among the sexes of D. sublineatus. Females tend to be more evenly elongate regularly oval, while males have a greater dorsoventral convexity in the scutellar region (especially evident in lateral view) resulting in a steepness in the humeral region of the elytra and the posterolateral region of the pronotum. Males of D. sublineatus also have the lateral margin, just posterior to the humeral region of the elytra, slightly expanded. As mentioned earlier females also have a medial exspansion of abominal sternite VII, not seen the males.
This species exhibits a large amount of variation throughout its range, with noticeable variation in body form. A series of specimens from near Tehuanatepec, Oaxaca, Mexico, has the females noticeably smaller than the males, and much more parallel sided in appearance, as well as both sexes with the elytral apices very flatly rounded, nearly truncate in appearance. A single female specimen from Salama, Guatemala (Fig.  46C) (UCRC), was observed with a highly parallel sided body form, with the elytral apices seemingly produced, and very flatly rounded. This specimen at first glance seemed like a different species, but the specimen possesses the well-developed elytral striae and abdominal sternite VII with a medial expansion, currently characteristic of only D. sublineatus. Without a male to unambiguously place the Guatemalan specimen as a different species, we considered it a variation of D. sublineatus, as it possessed the diagnostic females character of the medial expansion of abdominal sternite VII, thus far unique to D. sublineatus.
Specimens from Siera de Zapotan, Narayit, Mexico (Fig. 46A) (UCRC), show variation in the punctation of the elytra, being composed of large shallowly impressed punctures, giving the elytra a dimply appearance. This situation is also seen in specimens from this locality in D. solitarius (Fig. 46B). Other variation in the sculpturing of the elytra can be seen in several different populations. Some populations have the cells of the reticulation of the pronotal disc, as well as the elytral disc near the scutellar and sutural region, noticeably reflective, creating a bright metallic green color.
Even though there is a great deal of variability in these species in terms of body form, elytral apices, and elytral sculpturing, several characters are very stable. These include the strong development of the elytral striae in both sexes, in males the form of the aedeagus, and in females abomdinal sternite VII possessing a medial expansion. There is very minimal varation in the form of the male aedeagus, which is the most diagnostic character for species recognition within Dineutus. Diagnosis. Male (Fig. 47C-D): Size: 13.5-15.4 mm. Body form regularly oval; elytral apices truncate, lateral corner of truncation roundly angled, fine serration present apically, apicolateral margin without sinuation, elytral striae primarily indistinct, dense microreticulation covering entirety of elytra and pronotum, producing a polished metal feel, elytra often with violet iridescence; ulimate protarsus ( Fig. 30C) ca. 2× as long as wide; protibiae club-shaped; profemora with small acute sub-apicoventral tooth; mesotarsal claws ( Fig. 48C) without ventral margin expanded into weak denticle; venter darkly colored, usually black to dark reddish brown, mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen; Aedeagus (Fig. 48A, B, D) median lobe in dorsal view nearly evenly attenuated basally to apically, more strongly narrowed in apical 1/3, apex very shortly rounded, not acuminate, in lateral view median lobe ventrally weakly sinuate in apical 1/3, noticeably dorsally curved, ventrally median lobe with parallel sided sperm-groove, parameres as wide as base of median lobe apically, weakly laterally expanded in apical 1/3. Female (Fig. 47A-B): Size: 13.3-15.1 mm. Body form regularly oval; elytral apices truncate, lateral corner of truncation roundly angled, fine serration present apically, apicolateral margin without sinuation, elytral striae primarily indistinct, visible upon close examination, dense microreticulation covering entirety of elytra and pronotum, producing a polished metal feel, elytra often with violet iridescence; ulimate protarsus ca. 2× as long as wide; protibiae club-shaped; profemora without sub-apicoventral tooth; venter darkly colored, usually black to dark reddish brown, mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen. Differential diagnosis. Dineutus truncatus is unique among all other New World Dineutus in having the elytral apices truncate, with fine serration present apically, males with the ultimate protarsomeres (Fig. 30C) ca. 2× as long as wide, profemora with a small sub-apicoventral tooth present, mesotarsal claws with ventral margins not expanded into a weak denticle (Fig. 48C), and in the form of the male aedeagus (Fig.  48A). The species most similar to D. truncatus is D. mexicanus (originally described as a subspecies of D. truncatus by Ochs [1925a]). Both species have their elytral apices truncate, however only D. truncatus has the elytral apices with fine serration present, those of D. mexicanus have the serration much more blunt and thick and/or reduced, in some specimens down to only irregularities of the elytral apices. There is a general difference between the species in the dorsoventral convexity of the body form in lateral view. In general, D. truncatus tends to be noticeably more humped in the scutellar region with the posterior length of the elytra more dorsoventral depressed, while in D. mexicanus the posterior length of the elytra is less dorsoventrally depressed, giving D. mexicanus a generally less dorsoventrally convex lateral profile, without as much of a pronounced hump in the scutellar region.
Males of D. truncatus can further be separated from males of D. mexicanus by several characters. In D. truncatus the elytral striae, while present, are nearly indistinct and are weakly impressed, while in D. mexicanus the striae are evident just posterior to the middle of the elytra, disappearing laterally and before the elytral apices. The protarsi (Fig.  30) have several characters separating D. truncatus from D. mexicanus. The size of the ultimate protarsomere in D. truncatus (Fig. 30C) is ca. 2× as long as wide, while in D. mexicanus (Fig. 30A) the ulimate protarsomere is less than 2× as long as wide. The shape of the lateral margins of the protarsal tarsomeres 2-5 also differs among the species. In D. truncatus, in anterior view, the tarsomeres are laterally flatly rounded (Fig. 30C), this differs strongly from a specimen of uncertain species assignment from Oaxaca (see Figure 48. Dineutus truncatus. A aedeagus dorsal view B aedeagus ventral view C ♂ mesotarsal claws D aedeagus lateral view. Scale bar for C ≈ 0.10 mm all others ≈ 1 mm. specimens of uncertain placement below) in which the lateral margins of the protarsi in anterior view are roundly angled (Fig 30B), but are similar to those of D. mexicanus (Fig.  30A). The mesotarsal claws can also assist in separating the males of D. truncatus (Fig.  48C) from D. mexicanus (Fig. 29C), in that the ventral-margins lack an expansion forming a weak denticle. By far the most reliable way to separate the males of these species is by the form of the aedeagus. In D. truncatus (Fig. 48A) the median lobe of the aedeagus is nearly evenly tapered basally to apically, with the apex narrowly rounded and appearing highly pointed, as opposed to the being acuminate as in D. mexicanus (Fig. 29A).
Females of the species are primarily separated by the general differences listed between the species for elytral differences and body form differences. The size of the ultimate protarsomere in females shows similar ratios to the males being ca. 2× as long as wide in D. truncatus, while in D. mexicanus the ulimate protarsomere is less than 2× as long as wide.
Habitat. Lotic and lentic (Ochs 1949). The authors have collected this species from a medium sized stream with clear water, running through a small agrarian valley in Chiriquí, Panama. In the stream D. truncatus was found in areas outside of the rapids where the water slowed and pooled, such as the stream margins or behind large rocks in the stream.
Discussion. This species has the most southern range of any New World Dineutus being found only in Central America, as far south as Panama. It is unclear however, the true extent of the range of D. truncatus. In Panama, all specimens observed in this study were from the western half of the country near Soloy and Chiriquí, with most references in the literature for the distribution of D. truncatus in Panama only mentioning the latter locality (Sharp 1882; Ochs 1949). The north and western limits of this species' range is even less clear. The type locality is Chontales, Nicaragua, and the species is readily found in Costa Rica, but literature references also suggest the limits may be as far northwest as Guatemala andMexico (Sharp 1873, 1882;Ochs 1949). It is likely as previously suggest by Ochs (1949) that these data refer to D. mexicanus. Dineutus mexicanus is superficially very similar to D. truncatus in habitus and specimens determined to be D. mexicanus in this study included a female specimen from Guatemala, and others from as far southeast as El Salvador. As is often becoming the case in Dineutus, some very similar species have overlapping ranges with one having a very limited range of endemism relative to a another more widely ranging species. Dineutus truncatus follows this pattern in relation to D. mexicanus, seemingly only definitely being found in Nicaragua, Costa Rica, and western Panama. As is the case with other species with narrow ranges D. truncatus specimens were relatively few in number, and it is not well represented in many museums. ous region of the country. These records appear to suggest that D. truncatus may be restricted to mountainous regions, and may be a mountain endemic, similar to the situation possibly seen in D. mexicanus. It may be that the most southeastern extent of D. mexicanus' range is the Cordillera de Talamanca in Panama, and the northwestern most portion of its range may reflect Nicaraguan mountain ranges.
In Costa Rica where D. truncatus is very common it has been given the common name of "mamatetas" (Ochs 1949;Hogue 1993). The literal translation from Spanish appears to mean nipple sucker or nipple suckling. Ochs (1949) translated this name to "dug-sucker" which the second meaning for dug is nipple, in agreement with the translation. The reason for this common name does not appear to be known. Ochs (1949) says that Nevermann believed it to come from superstitious ideas, but does not elaborate, nor does Ochs (1949) provide a citation for Nevermann's interpretation, for further investigation. An interesting connection to the name mamatetas and the literal translation of nipple sucker, is the practice of some young girls in East Africa to use gyrinids to stimulate breast growth (Kutalek and Kassa 2005). Young girls allow gyrinids to bite their nipples in hopes of stimulating the breasts to grow larger, and interestingly, among the gyrinids in use are common African species of Dineutus (Kutalek and Kassa 2005). It is unclear, if there is any similar practice present in Costa Rica, thus resulting in the common name referring to breast suckling. Diagnosis. Male (Fig. 49A-B): Size: 17.45 mm. Body form regularly oval; elytral apices truncate, lateral corner of truncation roundly angled, blunt irregularities present apically, apicolateral margin weakly sinuate, elytral striae faint, elytra microreticulation present, apicolaterally with slightly bronzy appearance; ulimate protarsus ( Fig. 30B) less than ca. 2× as long as wide, with angled lateral margin after basal 1/3, remaining protarsi with rounded lateral margins; protibiae club-shaped; profemora with small acute sub-apicoventral tooth; anterior mesotarsal claw (Fig. 50C) with ventral margin expanded into weak denticle; venter darkly colored, reddish brown, mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen; Aedeagus (Figs 50A, B, D) with median lobe in dorsal view parallel sided, weakly laterally expanded in apical 1/4, apex shortly acuminate, ventrally with parallel sided spermgroove, parameres noticeably laterally expanded in apical 1/3, asymmetrical, in lateral view parameres constricted near mid-length.

Specimens of uncertain placement
Differential diagnosis. This specimen is different from all other New World Dineutus species examined in having truncate elytra with the lateral angle rounded, with weak  sinuation apicolaterally, and blunt irregularities present, the protarsus (Fig. 30B) has the lateral margin rounded, the ultimate protarsomere angled apically after the basal 1/3, and the form of the aedeagus (Fig. 50A). The aedeagus of this specimen is unique among Figure 51. Type specimens A Dineutus analis Régimbart, 1882 lectotype and labels B Dineutus discolor Aubé, 1838 lectotype and labels C Dineutus solitarius Aubé, 1838 lectotype and labels D Dineutus metallicus Aubé, 1838 lectotype and labels E Gyrinus longimanus Olivier, 1795 lectotype and labels F Dineutus truncatus mexicanus Ochs, 1925 holotype and labels. all known world species of Dineutus in having parameres that are medially strongly constricted in lateral view. Externally, however, the specimen is most similar to the North American species D. truncatus and D. mexicanus. It can be separated from D. truncatus by the shape of the elytral truncature and the shape of the male protarsi (Fig. 30). In this specimen the elytral truncature has the lateral angles rounded and the apex with blunt irregularities, instead of the lateral angles of the truncature acute, with fine serration present at the elytral apices as in D. truncatus. The length of the ultimate protarsomere is less than 2× the width, whereas in D. truncatus the length is approximately 2× the width.  This specimen and D. mexicanus have similar elytral truncature, and similar ultimate protarsomere size ratios, however the shape of the protarsus is very different. It (Fig. 30B) has the lateral margin of protarsomeres II-IV broadly rounded, whereas in D. mexicanus (Fig. 30A) they are more flatly rounded to subtruncate. The ultimate protarsomere of this specimen is strongly angled apically after the basal 1/3 (Fig. 30B), whereas in D. mexicanus it is evenly tapered basally to apically (Fig. 30A). Also, in this specimen the frontoclypeal suture is sinuate medially with a rounded posterior expansion, whereas in D. mexicanus the suture is mostly flat and only weakly angled medially. The mesotarsal claws are also slightly different, with those of of this specimen having a slightly more developed denticle.
Discussion. There are several characters that suggest this specimen represents a species distinct from D. mexicanus (see the diagnosis and differential diagnosis section above). The aedeagus of this specimen is strange, even among the world Dineutus fauna, as discussed above. While the aedeagus does appear to be asymmetrical in the parameres, suggesting a malformation, the rest of the body is highly symmetrical, without any noticeable deformities. Other specimens encountered that were clearly aberrant in some way, had asymmetrical features in the body, usually the prothoracic legs. Given the distinct characters discussed we have included the specimen here without placing it among any of the known species. However, as we only have a single specimen, and given its very odd genitalia, we have decided not to formally describe this species due to lack of additional material. Other Dineutus specimens examined from western and north central Oaxaca (IEXA) belonged to D. mexicanus. However, this specimen comes from a locality to the south separated by a mountain range, again suggesting it may indeed represent a species other than D. mexicanus. Hopefully future collecting near Tapanatepec, Oaxaca, Mexico will allow placement of this enigmatic specimen.

Checklist of the New World species of Dineutus
Dineutus amazonicus Hatch, 1930