Hydraena rubrifurcata, new species

Figs. 69 (habitus), 71 (aedeagus), 260 (map)

Type Material. Holotype (male): Antsiranana, 14.4354S 49.78E Sava, Marojejy NP, 1km along main path from Camp I to Camp II, forest stream with some pools, stones and dead leaves, elev. 590 m, 11 xi 2014, J. Bergsten, R. Bukontaite, J.H. Randriamihaja, T. Ranarilalatiana & S. Holmgren (MAD14-59) (NHRS). Paratypes (15): Same data as holotype (7 NHRS); Antsiranana, 14.4329S 49.7592E Sava Marojejy NP 500m W from Camp II, big rocky forest stream, elev. 640 m, 14° 25' S, 49° 45' E, 10 xi 2014, J. Bergsten, R. Bukontaite, J.H. Randriamihaja, T. Ranarilalatiana & S. Holmgren (MAD14-57) (7 NHRS); 14.4354S 49.768E Sava Marojejy NP 1km along main path from Camp I to Camp: forest stream with some pools, stones and dead leaves, elev. 590 m, 14° 26' S, 49° 46' E, 9 xi 2014, J. Bergsten, R. Bukontaite, J.H. Randriamihaja, T. Ranarilalatiana & S. Holmgren (MAD14-53) (1 NHRS).

Differential Diagnosis. Similar to H. bisinuata in size, habitus, and reddish brown color; differentiated therefrom by the carinate metaventral plaques and the slightly more strongly punctate dorsum. The aedeagi of the two species markedly differ (Figs. 60, 71).

Description. Size: holotype (length/width, mm): body (length to elytral apices) 1.73/0.74; head width 0.42; pronotum 0.39/0.55, PA 0.47, PB 0.47; elytra 1.07/0.74.

Labrum light brown. Dorsum of head dark brown to piceous; pronotum with transverse rectangular dark brown macula, surrounding areas light reddish brown; elytra and legs light reddish brown; maxillary palpi testaceous, distal ½ of last palpomere not darker.

Head with clypeus moderately finely and moderately densely punctate, microreticulate laterally; frons distinctly more coarsely punctate than clypeus, more densely punctate laterally where interstices narrow walls to 0.5xpd, interstices shining. Mentum and postmentum coarsely, densely punctate, rugulose, interstices shining. Genae raised, shining, with deeply demarcated posterior ridge, interrupted in midline.

Pronotum bisinuate; anterior margin straight behind eyes, emarginate behind frons; PF1 and PF2 absent; PF3 deep; PF4 moderately deep; PF3 and PF4 moderately deeply confluent.

Elytra weakly arcuate laterally; summit of moderately steep posterior declivity at ca. midlength; lateral explanate margins wide; serial punctures round, separated by ca. 0.5xpd or less, ca. same size as largest pronotal punctures. Intervals ca. 0.5xpd; discal intervals very weakly raised, if at all, shining. Apices in dorsal aspect rather sharply conjointly rounded, in posterior aspect margins not forming angle with one another.

Ratios of P2 width and plaque shape (P2/w/l/s) ca. 1/1/2/1. P1 width ca. 0.6x P2; median carina sinuate in profile. P2 l/w ca.1/1, sides converging posteriorly, apex blunt and on same level as anteromedian carina of metaventrite. Plaques narrow, roundly raised, converging anteriorly, width tapering from posterior to anterior, becoming carinate at anterior extreme, separated basally by ca. 2– 3x plaque width, located at sides of median depression. Metaventrite anteromedian carina strong, shorter than plaques, as 4 to 5, joining anterior of plaques, together forming inverted Y-shape; long and strong, slightly arcuate longitudinal ridge on each side, extended posteriorly from margin of each mesocoxal cavity. AIS width at arcuate posterior margin ca. 1x P2. First abdominal ventrite concave behind AIS. Protibia straight, slender. Mesotibia very slightly arcuate, medial margin over ca. middle 1/3 with 4 or 5 short sharp spines. Metatibia very slightly arcuate, if at all, in distal 1/3, slender. Metafemur moderately slender. Abdominal apex with very narrow, minute apicomedian notch.

Etymology. Named in reference to the reddish color and inverted Y-shaped carina of the metaventrite.