Hydrochus bisinuatus, new species

Figs. 1, 5

Type Material. Holotype (male): PERU: Loreto Prov., On the Amazon nr. the Shishista River, 400 m, 1 May 1992, leg. James Danoff-Berg, ex: at lights (SEMC) . Paratypes (4): PERU: Ucayali, Rio Calleria, 15 km from Ucalagi, 3–13.x.1961, leg. Borys Malkin (3 NMNH); Pucallpa, 10–12.iv.1969, leg. P. & P. Spangler (1 NMNH) .

Differential Diagnosis. Among known Peruvian species, differentiated from all, except H. astrictus, by the deep cervical groove behind the eyes. This species is a member of the H. collaris group (sensu Perkins 2019c); differentiated from the known other species in the group by the more sinuate anterior margin of the pronotum, and the smaller body size (ca. 2.74 mm). However, reliable determinations will require careful examination of the male genitalia (Fig. 5; described below).

Description. Habitus as illustrated (Fig. 5). Size: holotype (length/width, mm): body (length to elytral apices) 2.74/0.94; head width 0.68; pronotum l/w 0.32/0.33; PA 0.60; PB 0.49; elytra 1.66/0.94. Dorsum grey to silver, with moderately strong iridescence, elytra with black spots. Legs testaceous to brown, with tibiofemoral joints darker. Punctation on elytra ca. 2x that of pronotum. Elytra interstriae ca. 1–2x strial puncture diameter. Interstria 9 th more convex than others, overhanging 10 th interstria. Usual area of callus on 5 th well raised, moderately elongate, ca. 6 punctures in row on each side.

Head with deep curving cervical groove from side to side behind eyes, groove punctate, cervical area behind groove impunctate, shining, with very fine, low, closely set longitudinal raised lines.

Pronotum very slightly wider than long (as ca. 30/31), widest at anterior margin, narrowed at base, sides slightly sinuate, smooth; anterior margin sinuate, median ½ markedly arcuate, fitting into cervical groove; anterior angles slightly produced; depressions deep to moderately deep, much more densely punctate than reliefs between depressions, latter almost entirely impunctate.

Elytra with spaces between strial punctures ca. 1x their diameter; apices rather sharply conjointly rounded in dorsal view, in lateral view outer margin with distinct angulation, impunctate area of apices rather large.

Ventral characters: Mentum coarsely densely punctate, with median fovea. Submentum with two deep foveae, posterior margin arcuate.

Male genitalia (Fig. 5) general characters: genitalia elongate, about six times as long as widest part, basal piece slightly shorter than parameres; parameres in distal ½ much narrower than aedeagus, in proximal ½ slightly wider than aedeagus, paramere tips arcuate toward midline; aedeagus widest subapically, becoming narrower from agw to basal area; basal piece slightly wider in dorsal/ventral views than lateral view, in lateral view very slightly arcuate, lacking any process of sclerotized rim.

Dorsal surface: pdmm contiguous with, or only very narrowly separated from alm; adbl small; adtl very indistinct, if present.

Ventral surface: pvmm contiguous with, or only very narrowly separated from alm in distal ¾, proximal part overlapping alm slightly.

Etymology. Named in reference to the bisinuate anterior margin of the pronotum.