The types of Formicosepsis tinctipennis de Meij., 1916, and Lycosepsis metatarsata de Meij., 1924, have been studied, lectotypes are designated and redescriptions are given. The genus Lycosepsis Enderlein, 1920 is recognized as a subgenus of Formicosepsis de Meij., 1916. Within Formicosepsis s.str. two species groups are characterized, viz. the defecta-group and the tinctipennis-group. Three new species, F.(F.) defecta n.sp., F.(F) barbipes n.sp. and F.(L.) brincki n.sp., are described. Keys to recent genera of Cypselosomatidae s. str. and to subgenera and species of Formicosepsis are given. The genus Formicosepsis, with subgenera, species groups, and species, is described. The inclusion of Pseudopomyzidae in the Cypselosomatidae is discussed and questioned.