Two species of Gyraulus (Pulmonata: Planorbidae) new to the British Pleistocene

A specimen of Gyraulus riparius (Westerlund) has been detected in a sample of fossilferous fluvial silt of late Middle Pleistocene age from new sections exposed in the well known interglacial deposits at Histon Road, Cambridge. Several specimens of Gyraulus rossmaessleri (Auerswald) were recovered, together with a restricted fauna of other molluscs, from organic silts associated with an intraformational ice-wedge cast within fluvial gravels at Baston, Lincolnshire. These silts probably accumulated in a thaw pool that existed during an extremely cold episode in the middle of the last (Devensian) cold stage, a conclusion supported by other fossils and by a radiocarbon date of 31,570 +/- 510 yr BR Neither species lives in Britain today and neither had previously been recorded from the British Pleistocene.