[Proceedings of the symposium 'Molluscan Palaeontology' : 11th International Malacological Congress, Siena (Italy) 30th August - 5th September 1992 / A.W. Janssen and R. Janssen (editors)]: Early rissoid gastropods from the Jurassic of Italy: the meaning of first appearances

Studies of Jurassic outcrops from Veneto, Central Italy and Sicily improved our knowledge on the gastropods of these areas, characterised by the presence, aside of archaic forms, of some modern ones. Noteworthy is the record from those outcrops of several species, which can be referred to the family Rissoidae (Rissooidea). Formerly, earliest rissoid records were only known from European outcrops of younger age. In the Italian records several species have been recognised belonging to at least two genera of Rissoidae, namely Rissocerithium and Zebinostoma. The presence of such a relatively diversified number of species, bears witness of a well established group. They should have had a common ancestor with the Rissoina-like rissoids of the continental margins. Their diversification can be related to the peculiar characters of the Intra-Tethyan communities