RESUMEN
A morphological and molecular study of 17 Cylindrotomidae species revealed that the two subspecies of Cylindrotomadistinctissima, the Nearctic C.americana Osten Sacken, 1865, stat. reval. and the Palearctic C.distinctissima (Meigen, 1818), represent separated lineages and consequently are raised to species level. Cylindrotomajaponica Alexander, 1919, syn. nov. and C.distinctissimaalpestris Peus, 1952, syn. nov. are now known to be junior synonyms of C.distinctissima. Triogmakuwanailimbinervis Alexander, 1953, syn. nov. and T.nimbipennis Alexander, 1941, syn. nov. are now placed into synonymy under Triogmakuwanai (Alexander, 1913). The Japanese Cylindrotomidae are all redescribed and all available literature and distribution data are summarised. Supplementary descriptions and illustrations for male and female terminalia of Cylindrotomanigriventris Loew, 1849, Diogmadmitrii Paramonov, 2005, Liogmanodicornis (Osten Sacken, 1865), Phalacrocerareplicata (Linnaeus, 1758), P.tipulina Osten Sacken, 1865, and Triogmatrisulcata (Schummel, 1829) are provided. The following new distribution records are outlined; Diogmacaudata Takahashi, 1960 from Arkhangelsk Oblast, Russia; D.glabrata (Meigen, 1818) from Belarus, Latvia, and Altai Republic, Amur Oblast, Novgorod Oblast, Magadan Oblast, Samara Oblast, and Kuril Islands (Shikotan I and Paramushir I) in Russia; Liogmaserraticornis Alexander, 1919 from Khabarovsk Krai, Russia; Phalacrocerareplicata from Khabarovsk Krai, Russia; and the presence of Cylindrotomanigriventris in Altai Republic, Russia is confirmed.