East China, Zhejiang Province, Tiantongshan Mountain.

HOLOTYPE, male: ‘CHINA: ZHEJIANG Prov. / Ning’bo City / Tiantongshan Mt./alt. 350 m, 24–26.iv.2009/Ting FENG leg.’ (SHNU). PARATYPES: 4 males, 6 females, same label data as holotype (SHNU)

Male. Length 2.2–2.4 mm (Fig. 1). Reddish brown, maxillary palpi and tarsi lighter.

Head (Fig. 3) slightly wider than long, nearly triangular, covered with short hair on dorsal surface. Clypeus arcuate on anterior margin. Labrum (Fig. 5) longer than wide, with rows of long setae anterolaterally, anteromedian margin with four minute specialized setae. Mandible (Figs 6–7) with one large apical tooth and much smaller subapical tooth and row of median teeth on cutting edge; outer margin with long seta in apical one-third. Maxillary palpus (Fig. 8) with palpomere I minute, II pedunculate with anterior third broadened, III nearly triangular, IV predominately large, nearly fusiform. Labium (Fig. 9) slightly wider than long, rounded laterally, labial palpus composed of large basal segment and setae-like terminal segments; lateral lobe setose. Frons depressed between antennal tubercles. Vertex convex, with one pair of vertexal foveae connected by short U-shaped carina and with median keel. Eyes large and prominent, situated in basal two-fifths of head length, not emarginated, multifaceted, each composed of about 55 facets. Postgenae nearly rounded, with pair of lateral carinae extended to antennal tubercles. Gular area slightly depressed; gular foveae merged into single pit. Gular carina present. Antenna long and elongate, scape large, about 1.5 times as long as wide. Pedicle much smaller than scape, subcylindrical; antennomeres III–VIII each wider than long, transverse; club three-segmented with antennomeres IX–XI (Fig. 4) modified, roughly granulated. X about twice as wide as and 1.5 times as long as VIII, nearly triangular, X slightly longer than wide, inner side strongly concaved, with several short and thick setae; XI the largest, widest in the middle, inner antebasal part strongly protuberant.

Pronotum (Fig. 10) wider than long, lateral sides each with one median spine; with one pair of lateral and one pair of discal longitudinal sulci, one pair of antebasal spines near basal margin of pronotum, one pair of lateral antebasal foveae and two pairs of basolateral foveae distinct.

Elytra (Fig. 17) convex, longer than wide, narrowed toward base. Each tri-foveate; discal stria extended to half of elytral length; sutural stria present. Metathoracic wings (Fig. 11) fully developed, widest at middle, gradually narrowed from middle toward apex and base, apex rounded. Venter with clear pairs of lateral mesoventral foveae and lateral metaventral foveae.

Legs normal in structure. Mesotibia (Figs 12–13) with apical protuberance. Metatrochanter (Fig. 14) not spinose.

Abdomen with first visible tergite (morphologically tergite IV) largest, mediobasal foveae, basolateral foveae and basomedian cavity present; discal carinae very short; tergites V–VII successively shorter and narrower, each with pair of lateral foveae. Tergite VIII (Fig. 15) transverse, posterior side nearly flattened. Sternites IV–VII each transverse, successively shorter and narrower, each with pair of lateral foveae. Sternite VIII (Fig. 16) transverse, with anterior margin strongly emarginated and posterior margin flattened. Sternite IX (Fig. 18) membranous.

Aedeagus (Figs 20–22) with dorsal apophysis totally absent; parameres reduced, forming a ventral stalk with median lobe; endophallus elongate, very weakly sclerotized, gradually expanded posteriad; basal foramen large; basal bulb round posteriorly.

Female. Body size similar to male (Fig. 2). Antennal club not modified. Eyes smaller than in male. Metathoracic wing slightly smaller than in male. Mesotibiae not protuberant at apex. Tergite VIII (Fig. 17) semispheric. Sternite VIII (Fig. 18) transverse. Sternite IX reduced.

The specific name refers to the metatrochanter without any spine or protuberance.

The male genitalia of the new species is somewhat similar to that of Batrisodes or some species of Batrisus genus-group, and the male spine on the hind trochanter is absent in the new species, which makes the new species looks similar to Batrisodes in some male sexual characters. But it is still quite different from Batrisodes. The new species is placed in Tribasodites because of the following reasons: 1) the prothorax of the new species has basic characters (spinulate lateral margins) of the Tribasodes genus-group, which never occurs in the Batrisodes belonging to Batrisus genus-group (both genus-groups were defined by Nomura and Idris 2003), 2) its male genitalia is strictly asymmetrical, which does not match the symmetrical male genitalia of Batrisodes.

The new species is most close related to Tribasodites picticornis and Tribasodites antennalis by relatively large body size and sexually modified antennal club. Tribasodites spinacaritus can be readily distinguished by the absence of metatrochanteral spine on posterior margin and simple structure of aedeagus, while all the other species have spinulate metatrochanter and aedeagus with fully-developed dorsal apophysis.