Malacological evidence relating to the stratigraphical position of the Cromerian. The early Middle Pleistocene in Europe. Non-marine molluscan faunas from sites of late Lower and early Middle Pleistocene age in Britain, France, Germany and Denmark are reviewed. Conversely, two other prosobranchs, Lithoglyphus jahni and Fagotia wuesti , characteristic of the Bavelian and earlier periods, are absent in West Runton. These facts suggest that the two sites are close in age but that West Runton is the younger.
British sites assigned to the 'Cromerian' Stage fall loosely into three groups.
Group 1 is characterized by V. goldfussiana, T. runtoniana, Bithynia troscheli and Viviparus viviparus gibbus , and includes West Runton, Kessingland and Sugworth. The fauna of Group 2 with Valvata naticina, B. troscheli, Tanousia cf stenostoma and Belgrandia marginata is known only from Little Oakley. Group 3 faunas, such as those from Sidestrand and Trimingham, with V. naticina, Bithynia tentaculata and B. marginata , lack distinctive 'Cromerian' elements and have close affinities with certain Hoxnian assemblages. The extinct water vole Mimomys savini has been recorded from sites assigned to each of these three Groups. At Ostend, Norfolk, an undiagnostic molluscan fauna has been recovered from beds that have yielded the vole Arvicola t. cantiana .