Priochirus (Euleptarthrus) trifurcus

Priochirus (Euleptarthrus) trifurcus Wu & Zhou, new species

(Figs. 13–17)

Type material. Holotype: CHINA: Xizang: 3, Xizang, Motuo, Gedang, 2450 m, 5.iv.1980, Gentao Jin and Jianyi Wu coll. (SEM-CAS). Paratypes: CHINA: Xizang: 23, 3Ƥ, same data as holotype (SEM-CAS); 3, same label data except 2100 m, 6.iv.1980 (SEM-CAS).

Description. Body length 7.7–8.5 mm. HL 0.58–0.62 mm, HW 1.22–1.26 mm, PL 1.48–1.60 mm, PW 1.76–1.82 mm, EL 1.74–1.86 mm, EW 1.72–1.94 mm.

Coloration. Head black with mouthparts red-brown. Pronotum and elytra black or slightly red-brown.

Abdomen black except for posterior margine of 3rd–6th segments brown, posterior 1/3 of 7th and whole of 8th segment dark rufous. Antennae red-brown. Femora and tibiae red-brown, tarsi slightly rufous.

Head (Fig. 13) strongly transverse, about twice as wide as long, sides almost parallel; frontal impression deep, longer than wide, slightly narrowed frontad, width of its anterior margin about 1/6 times head width; median sulcus almost undistinguishable behind frontal impression, its lateral margins fused before posterior 1/4 of head; inner and outer lateral teeth distinctly pointed and of equal length, lateral impression between inner and outer lateral teeth triangular and deeply depressed; frontal angle of head distinctly convex and rounded; vertex distinctly covered with fine coriaceous ground sculpture, row of long setae along postero-lateral margin; eyes distinctly convex, occupying almost 1/2 length of head side. Clypeus moderately elongate, slightly rounded anteriorly, disc with two widely separated pairs of similar long setae, basal-lateral sides without lateral setae.

Mandibles (Fig. 14) almost symmetrical, moderately protruding, toward apex gradually bent inwards, 1st dorsal tooth distinctly projecting, introflexed and pointed, 2nd dorsal tooth only slightly convex in apical 1/4, apical tooth small with short seta close to its inner base, 3rd ventral tooth present and forming trifurcate structure with 1st and 2nd ventral tooth, mandible inner side deeply emarginate behind 3rd ventral tooth.

Mentum (Fig. 15) trapeziform, lateral margin ventrally convex, not interrupted at frontal angle, anterior margin broadly depressed in middle; median denticle small, slightly emarginate at apex, with narrow longitudinal keel along ventral side; ventral surface rugose with elongate basal impression bearing 3 basal setae, in central disc with long median seta, in front of which with moderate inverted Y-shaped anterior impression; 6–7 pairs of anterior setae arranged along latero-anterior margin, not extending to middle.

Antennae weakly geniculate, posteriorly barely reaching shoulder of elytra, 1st segment baculiform, apically emarginate, dorsally with indistinct shallow sulcus, 2nd smallest, slightly longer than wide, 3rd elongate and narrowed at base, about 2 times as long as 2nd, 4–6th slightly elongate ellipsoid, 7-9th quadrate, 10th slightly transverse, 11th elongate, bluntly pointed, about two times as long as 10th.

Pronotum slightly transverse, anterior margin weakly bisinuate, lateral sides almost parallel, posterior margin moderately protruding medio-posteriorly; superior marginal line continuous beyond posterior angle of pronotum and reaching the margined medio-posterior protrusion; disc surface covered with coriaceous ground sculpture, setiferous punctures sporadically scattered along superior marginal line, above these punctures, in anterior 1/3 of lateral marginal area with big setiferous punctures; median longitudinal sulcus very narrow, expanding at posterior end to form distinct fovea.

Protibiae crenulate externally, with 9–11 denticles, 2nd one slightly smaller than 3rd.

Elytra almost quadrate, sides slightly convex posteriorly, surface covered with coriaceous ground-sculpture more distinct than that on pronotum and head; along lateral margin several small sparsely scattered setiferous punctures.

Abdomen cylindrical, weakly broadened posteriorly; surface of 3rd–6th segments basally with dense isolated micropunctures, in posterior half with fine coriaceous sculpture, 3rd with row of setae along posterior margin, 4th–6th with two rows of setae, one along basal and the other along posterior margin, posterior setae longer and denser than basal; 7th and 8th segments densely covered by setae, except for glabrous median part.

Male aedeagus almost membranous (Figs. 16, 17) with median lobe bulbous at base, slightly constricted and squarely curved behind basal orifice, posterior part baculiform, weakly and broadly sclerotized on the dorsal side; parameres thin and slightly curved with their basal parts protruding ventrally and connecting to each other below basal orifice, in dorsal view this protruding structure pointed anteriorly; basal orifice rounded distally.

Remarks. The new species can be easily distinguished from other Euleptarthrus species by having two pairs of pointed lateral teeth on head and1st–3rd ventral teeth of mandible forming a trifurcate structure. Priochirus (E.) oxygonus also has two pairs of well developed lateral teeth on head, but can be easily distinguished from the new species by strongly projecting and sharp outer lateral teeth.

Distribution. Known only from the type locality in Xizang province, at elevation of 2100–2450 m.

Etymology. The species name, the Latin adjective “ trifurcus ” (trifurcate) indicates the shape of ventral teeth on its mandible.