Two new species of Desmopachria Babington, 1841 in the D. convexa species group (Coleoptera, Adephaga, Dytiscidae, Hydroporinae, Hyphydrini)

Abstract Two new species are described in the Desmopachria convexa species group in the Neotropical genus Desmopachria Babington: D. mancosp. nov. (Guyana), and D. mortimersp. nov. (Costa Rica). Two subgroups, the D. convexa-convexa and the D. convexa-signata groups are defined. Desmopachria convexa-convexa species are from North and Central America and have a subapical articulable lobe on the male lateral lobe that is large and elongate and extends well beyond the slender, oblique apex of the lateral lobe. Desmopachria convexa-signata species are from South America and have a subapical articulable lobe on the male lateral lobe that is small and discrete and does not extend beyond the truncate apex of the lateral lobe. The male genitalia of all recognized species in the D. convexa group are redrawn from the literature. New species are illustrated from specimens and described species have morphological features redrawn from published illustrations.


Introduction
The taxonomic situation concerning Desmopachria Babington was briefly reviewed most recently by Miller and Wolfe (2018;2019) and Braga & Ferreira Jr. (2018). Desmopachria is a species-rich genus of diving beetles restricted to the New World with numerous species described recently 2011;Gustafson and Miller 2012;Makhan 2012;2015;Megna and Sanchez-Fernandez 2014;Miller 1999;Miller and Wolfe 2018;2019). Currently the genus includes approximately 130 described species, and many more undescribed ones known to exist making it one of the larger genera of diving beetles in the New World.
Two new species are described here from the D. convexa species group which are characterized by an articulable appendage on the anterolateral surface of the male lateral lobe (Young 1980;. This group was reviewed by  with a number of species described subsequently ). The group is among the most widespread in Desmopachria, occurring throughout eastern North America south into southern South America.

Measurements
Measurements were made with an ocular scale on a Zeiss Discovery V8 dissecting microscope to 0.1 mm. The diagnostic range of measurements of structures was emphasized, so the largest and smallest specimens were preferentially measured to the extent possible. Measurements include: 1) total length (TL), 2) greatest width across elytra (GW), 3) greatest width of head (HW), and 4) distance between eyes (EW). The ratios TL/GW and HW/EW were also calculated.

Images
Illustrations were made using a drawing tube on a Zeiss Discovery V8 dissecting scope. Sketches were first done in pencil then scanned, placed into an Adobe Illustrator artboard and "inked" digitally using vector lines and modified with brushes.

Material
Specimens of Desmopachria were examined representing many species from all species groups including many from the following collections:

Taxonomy
The Desmopachria convexa group Diagnosis. The Desmopachria convexa group is characterized in the genus by an articulable subapical process on the male lateral lobe of the aedeagus and the male median lobe either apically bifid (e.g., Fig. 15) or trifid (e.g., Fig. 11) with the exception of D. pilosa Miller (apically simple, Fig. 52) and D. majuscula Young (seemingly absent, Fig.  34). The species are extremely similar to each other in external appearance, though there are some diagnostic variations in size, shape, punctation and coloration. But externally there are often few particularly useful characters for distinguishing closely related species. Males and females are externally extremely similar, as well.
There are two apparent subgroups in the D. convexa species group, those with a smaller subapical articulable appendage on the lateral lobe not extending beyond the truncate apex (e.g., Figs 4, 5) and those with a larger subapical articulable appendage that is leaf-like and extends well beyond the elongate, slender oblique apex of the lateral lobe (e.g., Figs 9, 10). These are referred to here as the D. convexa-convexa subgroup (with the larger subapical articulable appendage) and D. convexa-signata subgroup (with the smaller subapical articulable lobe). Desmopachria convexa-convexa species are found in North and Central America and the Caribbean, and D. convexa-signata species are found in South America. It is not clear at this time how these two groups might be related to each other or their monophyletic status, but they seem to be well-characterized by the shared articulable appendage of the male lateral lobes which is unique in Desmopachria and Dytiscidae in general.
Comments. This group corresponds to the Desmopachria convexa-grana group of Young (1980), which he later revised . Additional new species were described by several investigators ).
It is possible that several other described species may belong to this species group including D. attenuata Régimbart, 1895 (Young 1980), D. balfourbrownei , D. striga Young, 1990, and D. subfasciata Young, 1990 based on illustrations suggesting the presence of a subapical or apical articulable structure on the lateral lobe ). These species have not been well-described making the diagnostic characteristics of the group hard to discern. It does not appear that these species correspond with either of the new species described here, however. The paratype specimen was not dissected but it has the same color pattern, size, and other features as the holotype. It is assigned to this species even though it is from some geographic distance away.
Diagnosis. This is an extremely small species among Dytiscidae and even among Desmopachria ( Fig. 1; TL = 1.2-1.3 mm). The dorsal diffuse maculae on the elytra are characteristic (Fig. 1). The male genitalia include a dispositively diagnostic set of features (Figs 2-5) and place the species in the Desmopachria convexa-signata subgroup (see above). The median lobe is short (Figs 2, 3). In lateral aspect it is irregular in shape, medially expanded ventrally and with the apical portion slender, short, slightly curved dorsad and apically narrowly rounded (Fig. 2). In ventral aspect it is very broad, basally deeply U-shaped, apically deeply bifid, each ramus broad basally, apically narrowed and slightly curved laterad (Fig. 3). The lateral lobe in ventral aspect is elongate, broad, of subequal width throughout to a broadly truncate apex, with the subapical articulable lobe small and broad (Fig. 4). The lateral lobe in lateral aspect is very broad basally with the apex slender, subapically slightly expanded on the dorsal margin and apically sharply pointed with the subapical articulable process short and slender (Fig. 5).
Etymology. This species is named manco, after Manco, the younger bounty hunter in the Sergio Leone film "For a Few Dollars More".
Distribution. This species is known from two localities in Guyana, Region IX (Fig. 58).
Habitat. The type and paratype were collected in "detrital pools" and a "marshy area." Desmopachria mortimer sp. nov. http://zoobank.org/F8656CD2-3D92-4B2B-94DA-5B04F8F029EC Figures 6-10 Diagnosis. This is a moderately sized, somewhat elongate species of Desmopachria ( Fig. 1; TL = 1.7-1.9 mm). The dorsal coloration is characteristic with diffuse darker regions medially and extending laterally onto the surface of the elytron (Fig. 6). The shape of the male genitalia is diagnostic (Figs 7-10) and place the species in the Desmopachria convexa-convexa subgroup (see above). The median lobe is short (Figs 7, 8), and in lateral aspect it is irregularly broad basally with the apical portion slender, short and curved dorsally to a narrowly rounded apex (Fig. 7). In ventral aspect it is very broad, basally broadly U-shaped, apically deeply bifid, with each ramus slender and strongly curved medially (Fig. 8). The lateral lobe in ventral aspect is irregularly shaped, broad, with the apex narrowly truncate and with a subapical articulable lobe that extends well beyond the apex of the lateral lobe and is apically acuminate and sharply pointed (Fig. 9). The lateral lobe in lateral aspect is very broad basally with the apex slender, elongate, directed dorsad, and with the subapical articulable lobe elongate, curved and apically sharply pointed (Fig. 10).
Sculpture and structure. Head (Fig. 6) broad, anteriorly produced in broadly rounded margin; anterior margin of clypeus margined with conspicuous, continuous narrow bead; surface of head shiny, very finely and sparsely punctate, punctation slightly denser posteriorly; eyes large (HW/EW = 2.0); antennae short, scape and pedicel relatively large and rounded, flagellomere III long and slender, apically ex-panded, antennomeres IV-X short and broad, lobe at anterodorsal angle, antennomere XI elongate, apically pointed. Pronotum short, lateral margins short, slightly curved with narrow bead, bead wider medially, slightly angulate medially; surface shiny, nearly impunctate medially, more but sparsely punctate along anterior and posterior margins, punctation variable, fine to course. Elytron moderately broad, laterally broadly curved; surface shiny, more coarsely and evenly punctate than pronotum, punctation shallow and indistinct, of variable sizes. Prosternum extremely short, longitudinally compressed, medially slightly carinate; prosternal process slender anteriorly, with distinctive, small medial tubercle, apically short and broad, concave, apically broadly pointed. Metaventrite broad and evenly smoothly convex medially, surface shiny, with very few indistinct punctures, anteromedially with curved transverse carina between posterior margins of mesocoxal cavities; metaventrite wings extremely slender. Metacoxa with medial portion short, less than 1/2 length of metaventrite medially, metacoxal lines distinctly divergent anteriorly; lateral portion of metacoxa extremely large, anteriorly strongly expanded; surface shiny, evenly but shallowly and indistinctly punctate, punctures evenly distributed. Metatrochanter large, longer than ventral margin of metafemur anterior to metatrochanter apex; legs otherwise not noticeably modified. Abdomen with surfaces shiny and smooth, nearly impunctate.
Etymology. This species is named mortimer, after Colonel Douglas Mortimer, the older bounty hunter in the film "For a Few Dollars More".
Distribution. This species is known only from one locality in Costa Rica, Prov. Cartago (Fig. 58).