Prohercostomus Grichanov in Baltic Amber with a Key to Species of the Genus (Insecta: Diptera: Dolichopodidae)

Specimens of four species of the genus Prohercostomus from late Eocene Baltic amber are studied and illustrated. The presence of anterior preapical seta on mid and hind femora, setose scape of antenna and convex posterior mesonotum confirm the placement of the genus in the subfamily Dolichopodinae. Sympycnites Grimaldi et Cumming is raised from synonymy with Prohercostomus and associated with Peloropeodinae. Gymnopternus devinctus is excluded from the genus, whereas four species are considered doubtful. Prohercostomus is the only extinct genus placed in the extant subfamily Dolichopodinae and includes eight recognized species from Baltic amber. A key to recognizable species of Prohercostomus is proposed for the first time.