Thirty shells of Tamayoa (Tamayops) banghaasi (Thiele, 1927) from Ilha Grande, Rio de Janeiro, were analyzed with a stereomicroscop showing the following characteristics: discoid shell, without macrosculptures; ovate-lunate aperture without teeth. Thin, sharp and not-reflected lip; umbilicus with 1/5 of the shell's diameter; impressed suture, total whorls from 4 to 5.5; protoconch with 1.5 to 2 whorls; yellowish-amber, translucent and glossy periostracum. The morphology of the shells were discussed, as well as the shell's dimensions. The conchomorphological patterns are important for systematic studies of mollusks and this work presents data that can be used in future studies about the family.

A malacological survey has been done by the sênior author in Ilha Grande, State of Rio de Janeiro, since 1996. Up to this date the only freshwater gastropods found were specimens of Antillorbis nordestensis (Lucena, 1954). The snails were collected at a swampy area situated behind the late Penal Colony Cândido Mendes (Ilha Grande Prison).