Marine and terrestrial molluscs are recorded from a coastal dune deposit in SW Morocco. The geological setting and the faunal content of the site suggest an Upper Pleistocene age. Most abundant were shells of the genus Theba which fell into three groups by means of qualitative, metric, and landmark analyses. Theba subdentata, a small form of T. chudeaui, and a new species T. tantanenis sp. nov. document the former co-existence of three species of Theba in a now desert-like part of the NW African coast.