Diagnosis: Head with frontal furrows deep, flattened and indistinct at level of hind suborbital seta in some species, +/- strongly curved at middle. Frons and supraorbital areas strongly convex. Temples distinctly pubescent. Mandibles normal. Pronotum subcordate, with hind angles well produced. Pronotal base rectilinear or the outer fifth slightly curved anteriorly. Basal transverse depression of pronotum diffuse, limited towards disc; laterobasal foveae broadly developed. Pronotal median line distinct, but not deepened before base. Hind wings reduced to small stubs. Humerus broadly rounded. Each elytron with parascutellar seta, preapical seta and two discal setae on third interval, with anterior discal seta located on stria III at the end of the anterior elytral quarter, and with middle dorsal seta located on stria III somewhat behind elytral middle. Stria VIII slightly (T. dacatraianus, T. damchungensis) or faintly impressed behind the level of the fifth umbilicate pore and deeply impressed at levels of seventh and eighth umbilicate pores. Recurrent elytral preapical sulcus deeply impressed and directed to the end of the fifth stria. Ventral surface smooth. Legs average, with moderately slender (T. hodeberti, T. mieheorum sp. n.) or thick femora and relatively thin tibia and tarsi; protibiae distinctly dilated towards apices, hardly bowed, each without a longitudinal groove on external surface. Two basal protarsi of male dilated, dentoid at the inner apical border. Aedeagal median lobe average to large, with basal bulb spherically enlarged and strongly bent downwards, with basal velum small or completely reduced, and with terminal lamella strongly hooked at tip. Internal sac with sclerotized portion quadripartite, extending almost half of the length of median lobe or even more; folding lobes in dorsal view bilaterally symmetrical, whereas the more basal pair of lobes forms a sheath for the more distal pair. Parameres average to relatively stout, broad at tip, both with four setae; left paramere slightly longer than right one.

Remarks: Although this group includes species with relatively different external morphology, it is very likely a natural group because all the species share a more complicated structure of the internal sac of the aedeagus which is unique within the Trechus fauna of Tibet and adjacent mountainous regions, and is certainly a synapomorphic feature. However, the taxonomic position of the T. dacatraianus group within the genus is quite difficult to trace without taking into account a much more comprehensive data set of characters. Therefore, a more detailed phylogenetic study which includes the highly diverse Trechus fauna of the Western Chinese mountain ranges is needed.

Species included: T. bastropi sp. n. (South Central Tibet), T. dacatraianus Deuve, 1996 (North Eastern Tibet), T. damchungensis Deuve, 1997 (Eastern Tibet), T. hodeberti Deuve, 1997 (South Central Tibet), T. mieheorum sp. n. (South Central Tibet).