The genus Trichomasthus Thomson is defined and a key is provided to 19 Palaearctic species. Five new species from Soviet Far East are described by Sharkov: T. extimus sp.n. and T. leptocerus sp.n. from Kurile Islands, T. ortivus sp.n. from Primorsky Territory, and T. sachalinensis sp.n. and T. storozhevae sp.n. from Sachalin. T. terebratus sp.n. from Yugoslavia is described by Jensen. All the species are described or redescribed in the same way.