| Abstract: | In the course of researches on the fauna of «calcaires bajociens á bryozoaires of Aveyron départment (France), numerous collects of shells named Rhynchonelloidea ruthenensis (Reynès), type-species of genus RhynchonelloideaBuckman, in two localities enabled to do a morphologic study of this species with populations analysis. Internal characters have been shown both by serial sections and by direct observation of dissected shells. A comparison of genus Rhynchonelloidea and Homoeorhynchia, till now either distinct or considered synonymous according to authors, has been realised. Internal characters of Homoeorhynchia acuta (Sow.) have been precised. The two genus are distinct by beak and foramen's characters, by presence or lack of costulation on the beak and dorsal umbo, by the number of ribs, by presence or lack of septalium and by the development of median dorsal septum.The stratigraphical range of R. ruthenensis is:Upper Toarcian, Aalensis zone-Lower Aalenian, Opalinum zone. |
