Plastus Plastus biconcavus Wu & Zhou

Wu, Jie & Zhou, Hong-Zhang, 2010, Taxonomic study of subgenus Plastus s. str. (Coleoptera, Staphylinidae, Osoriinae) in China, with descriptions of five new species, ZooKeys 51, pp. 17-32 : 23-25

Plastus Plastus biconcavus Wu & Zhou sp. n. Figs 2712

Type material.

Holotype male, Guangxi: Longsheng: Neicujiang, 840 m, 7.vi.1963, Shuyong Wang coll. (IZ-CAS).

Description.

Measurement.Body length: 9.84 mm. HL: 0.71 mm; HW: 1.48 mm; PL: 1.56 mm; PW: 2.07 mm; EL: 2.18 mm; EW: 2.09 mm.

Coloration.Head black with labrum red-brown, mandibles black with inner side reddish brown (Fig. 7). Pronotum and elytra slightly dark brown (Fig. 2). Abdomen black except for 8th segment slightly rufous. Antennae dark red brown. Femora and tibiae slightly dark red brown. Tarsi brown.

Structural attributes.Head transverse (Fig. 7), twice as long as wide, sides slightly concave in middle; frontal impression strongly transverse, about 5 times as wide as median length, anterior margin almost straight in middle, posterior margin slightly rounded posteriorly; lateral teeth blunt and straightly projecting, middle of ventral side with bluntly convex subsidiary denticle, on inner side with row of 4-6 long setae extending onto anterior margin of frontal impression; lateral impression narrow, along posterior half of external side of lateral tooth, almost not reaching anterior margin of frontal angle of head, bearing 3 or 4 short setae; anterior margin of frontal angle of head rounded, without tooth; median sulcus on vertex about 3 times as long as median length of frontal impression, gradually broadened posteriorly, but abruptly divergent at posterior 1/4, posterior end of which almost twice as wide as middle; clypeus steeply inclined and rounded anteriorly, with shallow depression behind anterior margin, baso-laterally with 2 or 3 long setae; eye glabrous and convex, almost occupying half side of head; vertex broadly convex, between frontal angle and base of lateral tooth with luniform depression, in depressed region near posterior margin of frontal impression with two distinct punctures in line on each side of median sulcus, surface polished and evenly covered with fine micropunctures, along lateral and postero-lateral margin with some scattered punctures and long setae, at each side of posterior end of median sulcus without distinct fovea.

Antennae subgeniculate, antennomere I baculiform and apically slightly depressed, antennomere II smallest, slightly transverse; antennomere III elongate about 2 times as long as II; antennomeres IV quadrate; antennomeres V–X gradually more transverse apically; antennomere XI elongate, apically rounded, about 2 times as long as X.

Mentum trapeziform (Fig. 12), frontal angle slightly rounded, anterior margin weakly depressed in middle, with small indistinct median denticle, ventral surface with three transverse and waved ridges, but third indistinct and vague, space between ridges setose and rugose, but disc between last posterior ridge and basal margin glabrous and polished, with two large setiferous punctures on sides.

Pronotum transverse, distinctly wider than head, anterior margin weakly bisinuate, sides almost parallel, median longitudinal sulcus deep, broadest in middle and gradually narrowed anteriorly and posteriorly, not reaching either anterior or posterior margins; lateral marginal area with 21-23 setiferous punctures, punctures on upper half not distinctly larger than on lower, disc polished, surface evenly with fine micropuncture scattered, centrally with two distinct fovea on sides of longitudinal sulcus.

Protibiae externally furnished with 13 or 14 denticles, which gradually become shorter basally.

Elytra slightly longer than wide, epipleural line complete, setiferous punctures on lateral marginal side sparser and less distinct than those on side of pronotum.

Abdomen cylindrical, along anterior and posterior margin of III–VI segments respectively with row of setae, segments VII and VIII densely setose, disc of III–VI segment densely punctured, except for broad and transverse glabrous region near posterior margin, basal denser than apical, central disc of VII evenly punctured, VIII centrally with narrow longitudinal glabrous region.

Remarks.

This new species can easily be distinguished from other members of the subgenus Plastus s. str. by its strongly transverse frontal impression (about 5 times as wide as long) and two distinct foveae on sides of pronotal disc. Plastus Plastus taprobanus (Cameron, 1930) also has strongly transverse frontal impression and distinct fovea on either side of pronotum, but its lateral teeth are distinctly shorter than those in this new species.

Distribution.

Known from the type locality in Guangxi, elevation of 840 m.

Etymology.

The species name is derived from Latin words ‘bi-’ (double) and ‘concavus’ (concave) to indicate two distinct fovae on pronotum of this species.