On relict hydrobiid species in Brazilian Amazonia (Gastropoda, Prosobranchia, Hydrobiidae)

Two extant hydrobiid species from the lower Tapajos river of Brazil are redescribed. Potamopyrgus amazonicus Haas, 1949, is assigned to the genus Dyris Conrad, 1871. At least eleven species from Miocene deposits of Western Amazonia are assigned to Dyris, a genus that was previously assumed to be extinct. The apertural features of Sioliella effusa Haas, 1949, are considered indicative of a close relationship to Miocene Amazonian taxa formerly assigned to Eubora Kadolsky, 1980. Sioliella ovata spec. nov., a Miocene species resembling S. effusa is described. The two Tapajos species can be regarded as relicts of a speciose, endemic, Miocene Western Amazonian molluscan fauna.