Taxonomy of Guatemalan water beetles in the genus Hydrochus (Coleoptera: Hydrochidae) Perkins, Philip D. Acta Entomologica Musei Nationalis Pragae 2020 2020-04-23 60 1 291 301 8Y4RH Perkins, 2020 Perkins 2020 [975,1196,189,213] Insecta Hydrochidae Hydrochus Animalia Coleoptera 8 299 Arthropoda species sinuatus sp. nov.  ( Figs 1, 6)    Typematerial.HƟĿƟŦYPൾ:male ( NMNH):‘ GUATEMALA, 20 Mi. SW Puerto Barrios VIII-16-1965Paul J. Spanglerʼ.   Differential diagnosis.Among Guatemalan species,  H. sinuatusis recognized by the combination of moderately small size (ca. 2.39 mm), the densely coarsely punctate pronotum, and the male genitalia ( Fig. 6; described below). This species has a generalized  Hydrochushabitus; reliable determinations will require dissection of males.   Description.Habitus as in Fig. 6. Size (in mm): holotype: body (length to elytral apices / width) 2.39 / 0.89; head width 0.58; pronotum length / width 0.53 / 0.55; PA 0.53; PB 0.48; elytra 1.52 / 0.89. Body size moderate. Dorsum black, with moderately strong iridescence, elytra with non-iridescent black spots. Legs dark brown, with tibiofemoral joints slightly darker. Punctation on elytra ca. 2–4× that of pronotum. Elytra interstriae ca. 0.5–1.0× strial puncture diameter. Interstria 9 thmore convex than others, overhanging 10 thinterstria. Callus on usual area of 5 thinterstria small, weakly raised.  Fig. 7.  Hydrochus steineri sp. nov., habitus and male genitalia of holotype. Pronotum length slightly less than width, widest just behind anterior angles, narrowed at base, sides very slightly sinuate, minutely denticulate; anterior margin bisinuate; depressions, especially anteromedian, deep, reliefs sharply raised, depressions more densely punctate than reliefs. Elytra with spaces between strial punctures ca. 0.5–1.0× their diameter; 3 rdinterseries slightly raised over basal fourth; 4 thinterseries raised in area anterior to callus of 5 th; apices rather sharply conjointly rounded in dorsal view, in lateral view with submarginal row of large punctures, bordered above by low ridge, outer margin with strong angulation. Male genitalia ( Fig. 6). General characters: paramere tips slightly widened, distal ends pointed, lateral margins arcuate, medial margins of tips emarginate and well separated from lateral margins of aedeagus, distal end of tips extending very slightly beyond aedeagus, in lateral view tips narrow, sharply pointed; pwsadistinctive; aedeagus moderately narrow in both dorsal/ventral and lateral views, in dorsal/ventral views margins sinuate, distinctly narrowed slightly past midlength in dorsal/ventral views, with narrowly sclerotized lateral margins; basal piece shorter than parameres, with rim of orifice strongly sclerotized. Dorsal surface: adtllocated slightly distal to midlength; pdmmnarrowly overlapping almover basal two-thirds, then markedly arcuate where paramere tips begin; adbllarge, distinctively shaped. Ventral surface: pvmmvery slightly overlapping alm at base.   Etymology.Named in reference to the shape of the parameres and aedeagus, which have sinuate lateral margins. Adjective.