Hydraena triaequalis, Perkins, 2017

Perkins, Philip D., 2017, Hydraenidae of Madagascar (Insecta: Coleoptera), Zootaxa 4342 (1), pp. 1-264 : 77-78

Hydraena triaequalis , new species

Figs. 66 (habitus), 68 (aedeagus), 259 (map)

Type Material. Holotype (male): Fianarantsoa, Ranohira, helocrene with gravel areas in the valley upstr. ' Isalo Ranch' , elev. 780 m, 22° 26' S, 45° 21' E, 26 ix 2001, Gerecke & Goldschmidt (MD 98) ( NMW) . Paratypes (3): Same data as holotype (2); Fianarantsoa, Ihorombe : Isalo NP: 300m into the canyon de Makis: S 22.48655 E 45.37966, canyon river with side pools, elev. 700 m, 22° 29' S, 45° 23' E, 13 xi 2012, R. Bukontaite & J.H. Randriamihaja ( MAD12-03 ) (1 NHRS) .

Differential Diagnosis. The density of the pronotal and elytral punctures approximates that of H. amplipunctata , but the habitus of the two species differ markedly. H. triaequalis is unusual in that the widths of the head, and the anterior and posterior margins of the pronotum are equal. The aedeagus is immediately recognized by the extremely wide paramere.

Description. Size: holotype (length/width, mm): body (length to elytral apices) 1.59/0.65; head width 0.40; pronotum 0.37/0.47, PA 0.40, PB 0.40; elytra 1.00/0.65.

Dorsum with head dark brown to piceous, remainder of dorsum dark brown; legs brown; maxillary palpi light brown, distal ½ of last palpomere not darker.

Head with clypeus moderately finely and moderately densely punctate, effacedly microreticulate; frons coarsely densely punctate, interstices narrow walls to 0.5xpd, very weakly shining. Pronotum coarsely densely and deeply punctate, interstices narrow walls, shining. Mentum sparsely, moderately coarsely punctate, interstices shining; postmentum microreticulate in median depression, surrounding area shining. Genae raised, shining, with posterior ridge delimited by row of large punctures, interrupted in midline.

Pronotum distinctly sinuate laterally, almost subcordate; anterior margin straight behind eyes, emarginate behind frons; PF1 and PF2 absent; PF3 and PF4 deep, confluent.

Elytra weakly arcuate laterally; summit of posterior declivity near midlength; lateral explanate margins narrow; serial punctures round, separated by narrow walls, slightly smaller than largest pronotal punctures. Intervals narrow walls, weakly if at all raised, very weakly shining. Apices in dorsal aspect conjointly rounded, in posterior aspect margins do not form angle with one another.

Ratios of P2 width and plaque shape (P2/w/l/s [anteriorly]) ca. 1/0.2/2.5/1. P1 as wide as P2; median carina very weakly sinuate in profile. P2 l/w ca. 1.5/1, sides converging slightly posteriorly, apex blunt and on same level as anteromedian carina of metaventrite. Plaques very narrow, carinate lines, converging anteriorly and joining anteromedian carina, together forming inverted Y-shape, separated basally by ca. 5x plaque width, located at sides of deep median depression. Metaventrite anteromedian carina strong, slightly shorter than plaques; long longitudinal and slightly arcuate ridge on each side, extended posteriorly from margin of each mesocoxal cavity, almost attaining metacoxal cavity. AIS width at arcuate posterior margin ca. 1.5x P2. All tibiae straight, slender. Mesotibia with small subapical notch on medial margin. Metafemur slender, arcuate on lateral margin, very weakly sinuate on medial margin. Abdominal apex with very small apicomedian notch.

Etymology. Named in reference to the equal widths of the head and the anterior and posterior margins of the pronotum.