Bolbochromus Boucomont, 1909

Li, Chun-Lin, Yang, Ping-Shih, Krikken, Jan & Wang, Chuan-Chan, 2013, Three new species of Bolbochromus Boucomont (Coleoptera, Geotrupidae, Bolboceratinae) from Southeast Asia, ZooKeys 290, pp. 39-54 : 42-43

Genus Bolbochromus Boucomont, 1909

Bolbochromus Boucomont 1909: 117. Type species: Bolboceras laetus Westwood, 1852, by subsequent designation ( Paulian 1945).

Description.

The following generic description is primarily based on the examination of continental Bolbochromus species. Length 5.8-13.0 mm. Dorsum glossy, color black to dark reddish brown, usually with brownish yellow or reddish brown markings on surface of pronotum and elytron varying in number, size and shape inter/intraspecifically. Head: Surface overall coarsely punctate. Clypeus with anterior border transversely arcuate or subtrapezoid with lateral border rounded; anterior margin unarmed or with tubercles/horns varying in number (1 or 3) and size. Frontal horn small to reduced. Antennal club with first antennomere mostly glabrous and polished on inner side; club ovoid in shape, apparently decreased in size apically, club segments slightly curved outwardly. Eye small in dorsal view, canthus broadened, rounded at anterior margin, entirely dividing eye into dorsal and ventral parts, ventral part larger than dorsal part. Thorax: Pronotum unarmed or with small anterior discal quadrituberculate carina; surface unevenly punctate, punctures usually large, deeply impressed at sides; form generally widest at middle, disc vaulted, apical declivity steep or gradually declined anteriorly; midline usually distinctly indented and punctate; lateral fovea poorly to moderately developed; anterior margin evenly arcuate; basal margin not beaded at middle. Middle coxae narrowly separated by metasternal process. Elytron: With 7 or 5 punctate striae between suture and humeral umbone, first stria curving along side of scutellum and reaching elytral base with first interval tapering basally; stria 5 not reaching base of elytron or vanishing together with stria 2 when intervals 2, 3 and 5, 6 fused completely; disc with 7, 5 or 3 impunctate intervals between suture and humeral umbone, longitudinally convex in varying degree, interval 2 usually more flat and narrower than others, interval 5 and 6 fused at base. Legs: Protibia with 6-10 contiguous teeth on outer margin. Male genitalia: Overall unevenly sclerotized, complex. Parameres symmetrically elongate or capsule-like in shape, membranous or well sclerotized laterally with median membranous parts, usually longer than basal piece, surface sparsely punctate, glabrous or setose with varying length of setae, apex usually rounded, in some species curved ventrally. Median lobe well developed, degree of sclerotization usually stronger than parameres, mostly trilobate and significantly varying in shape by species, trilobate median lobe consisting of dorsal sclerite and paired lateral sclerites articulated by paired supporting sclerites at base, lateral sclerites connected laterobasally to parameres. Internal sac embedded in median lobe, unarmed and hardly visible. Temones paired, tapered apically with articulation to base of median lobe, greatly varying in length, shape and degree of sclerotization interspecifically. Basal piece unevenly sclerotized, apical portion usually asymmetrical in shape. Genital capsule well developed.

Remarks.

Bolbochromus species shows little sexual dimorphism as compared with species of Bolbelasmus and Bolbocerosoma . The latter two genera have their major sexual dimorphisms in the frontal and pronotal protrusions. In contrast, the shape of frontal and pronotal protrusions in Bolbochromus species is identical between males and females. Both sexes in Bolbochromus species have slight morphological differences in the anterior margin of the labrum, the secondary punctures on the pronotal disc, and the apical tooth of the protibia, thus making it difficult to separate males and females.

Key to males of Bolbochromus species occurring in Indochina and the Malay Peninsula