All from large muddy salting pool on upper Dee Estuary, Flintshire, salinity 29 p.p.t. (variable), replenished at high water spring tides and by fresh water seepage from Phragmites bed on landward side. The great majority of specimens collected had shallow sutures and flattened whorls. A few, like the two at bottom right had deep shell sutures and rounded whorls and were small, though adult.
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