Nomenclatural notes on the names of several species in the family Gyrinidae are provided. Six specific names are found to be junior homonyms. Three of them are replaced by nomina nova: Aulonogyrus marginatus (Aubé, 1838) by Aulonogyrus charlesaubei nom. nov., Gyrinus dubius Wallis, 1926 by Gyrinus suspectus nom. nov., and Macrogyrus (Andogyrus) colombicus australis (Brinck, 1977) by Macrogyrus (Andogyrus) colombicus brincki nom. nov. The other three junior homonyms were never considered congeneric with senior homonyms after the year 1899, and thus cannot not be replaced by new names: Gyretes dorsalis (Brullé, 1837), Macrogyrus australis (Brullé, 1835), and Andogyrus glaucus (Aubé, 1838); it is proposed that these names will be conserved by a ruling of the International Commission on Zoological Nomenclature. It is found that Enhydrus sulcatus (Forsberg, 1821) is a primary homonym and a junior subjective synonym of Enhydrus sulcatus (Wiedemann, 1821) in Wiedemann & Germar (1821). The neotype is designated for Gyrinus striatus Fabricius, 1792, which is a senior primary homonym and a senior subjective synonym of G. striatus Olivier, 1792 (both currently in Aulonogyrus Motschulsky, 1853). Gyrinus striatus was published by Olivier not only in 1792, but again in the year 1795 (so far treated as the correct publishing year). To stabilise the nomenclature, one and the same specimen is designated simultaneously as the neotype for Gyrinus striatus Olivier, 1792, and G. striatus Olivier, 1795, and thus both names become objective synonyms. Gyrinus ovatus Klug, 1829 is a senior subjective synonym of Gyrinus gibbus Aubé, 1838 syn. nov. and of Gyrinus apicalis Sharp, 1878 syn. nov. Gyrinus racenisi Ochs, 1953 must be used as the valid name for Gyrinus ovatus sensu Aubé (1838b) (nec Klug 1829). Lectotypes are designated for Gyrinus apicalis Sharp, 1878, Gyrinus gibbus Aubé, 1838, Gyrinus ovatus Klug, 1829, and Gyrinus paykulli Ochs, 1927b. Type specimens and diagnostic characters are illustrated for G. striatus Fabricius, G. striatus Olivier, G. ovatus Klug, G. racenisi and G. paykulli.