David Robinson kindly sent me a photograph taken in June 2013 at an unspecified location in the Sierra de Bahoruco, Dominican Republic. It is Coloniconcha prima Pilsbry, 1933, on which I devoted a paper in 2010. Note the peculiar shape of the tail as the snail crosses a depression of the rock on which it moves. It is able to cross gaps up to 5 cm (Breure 2010: 82).
Breure, A.S.H. (2010). The redicovery of a semi-slug: Coloniconcha prima Pilsbry, 1933 (Gastropoda, Pleurodontidae) from Hispaniola. — Basteria 74: 78-86.