Gastropods of the southwestern Atlantic genus Antistreptus Dall, 1902 from extant and Neogene deposits are reviewed. Fossil specimens come from the Punta Entrada Member of the Monte León Formation (50°21′25.4″S, 68°53′05.9″W). Extant samples are from museum collections and two expeditions on board the R/V “Puerto Deseado” to Burdwood Bank (54°13.934′S, 66°30.997′W) and surroundings. Dissection of soft parts and study of the type material of A. magellanicus Dall, 1902, Euthria (Glypteuthria) contraria Strebel, 1908, and A. rolani Castellanos, 1986 reveal that the latter two nominal species are synonymous. Neogene material assigned to the same genus could not be distinguished as a different species. According to the stratigraphic occurrence of the fossil material, the life-span of the genus Antistreptus Dall, 1902 and the species A. magellanicus Dall, 1902 is ~22 Myr, similar to that of the bivalve Cyclochlamys argentina Pastorino and Griffin, 2018.