Hydraena acumena Perkins 2011, new species

(Figs. 79, 81, 466)

Type Material. Holotype (male): Eastern Highlands Province: Koma River, tributary of Fio River, 100 m downstream of rattan bridge crossing, ca. 3.8 km S by E of Herowana airstrip, washed from margins of small pool of a steep, rocky, forest stream at confluence with river; gravel, cobbles, wet rock microhabitats, 1100 m, 6° 40' S, 145° 12' E, 31 v 2004, N. Porch (ANIC). Paratypes (4): Eastern Highlands Province: Same data as holotype (1 ANIC); Crater Mt., trek Haia–Wara Sera, 500 m, 6° 38.517' S, 145° 6.097' E, 12 ix 2002, Balke & Sagata (PNG 7) (1 NHM, 2 ZSM).

Differential Diagnosis. Similar to H. tetana in habitus, size, plaques, and some male sexual dimorphisms (tubercle on first abdominal ventrite, meso- and metatarsi with long hair-like setae (Figs. 66, 79); differing therefrom by slightly finer dorsal punctation and shape of the male protibial apex. Reliable determinations of the two species will require examination of the aedeagi, which distinctively differ (Figs. 68, 81).

Description. Size: holotype (length/width, mm): body (length to elytral apices) 1.65/0.65; head 0.27/0.36; pronotum 0.39/0.46, PA 0.39, PB 0.37; elytra 0.98/0.65. Dorsum piceous; legs and maxillary palpi dark brown.

Frons punctures ca. 1xef, slightly larger near eyes than medially; interstices shining, 1–6xpd. Clypeus microreticulate laterally, very finely sparsely punctate medially. Mentum very sparsely very finely punctulate, shining; postmentum densely micropunctulate, dull. Genae raised, shining, without posterior ridge. Pronotum cordiform, median 2/3 of anterior margin emarginate; punctures on disc ca. 1xpd those of frons, interstices shining, 2–6xpd, punctures slightly larger and denser at anterior and posterior; PF1 absent; PF2 very shallow, obsolete; PF3 deep; PF4 absent.

Elytra with summit of posterior declivity at or very near midlength; lateral explanate margins moderately wide; on basal 1/3 punctures ca. 1xpd largest pronotal punctures, some punctures subserial, punctures becoming gradually smaller toward posterior. Intervals not raised, shining, on disc ca. 2–3xpd, as are interstices between punctures of a row. Apices in dorsal aspect separately rounded, in posterior aspect margins forming moderately deep angle with one another.

Ratios of P2 width and plaque shape (P2/w/l/s) ca. 3/4/10/1. P1 laminate; median carina sinuate in profile. P2 raised, l/w ca. 2/1, sides slightly converging toward blunt apex. Plaques very large, very narrowly separated, slightly more narrowly separated posteriorly than anteriorly, weakly raised. Metaventrite without midlongitudinal ridge. AIS width at straight posterior margin ca. 1.7x P2. All legs long and very slender. Profemur (male) with small, sharply pointed tubercle next to trochanter. Protibia appearing compressed at ca. distal 1/3, then markedly, roundly widened on anterior surface, widened area with row of short spines on medial low ridge, and cluster of spines apically; lateral surface slightly emarginate. Mesotibia very slightly arcuate. Metatibia straight. Meso- and metatarsi with long hair-like setae along lower margin of basal tarsomeres. First abdominal ventrite with sharp tubercle in midline. Fifth abdominal ventrite simple. Abdominal apex symmetrical; last tergite (male) deeply notched. Aedeagus as illustrated (Fig. 81).

Etymology. Named in reference to the sharply pointed process on the midline of the first abdominal ventrite of males.

Distribution. Currently known from two very narrowly separated localities at the border of southeastern Area 1 and Area 13; elevation range 500–1100 m (Fig. 466).