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MOLLUSCS B. PELECYPODA Unto piclorum (Linn.). Not common : Stockerston Brook — tumidus, Retz. Not common : Stockerston Brook Anodonta cygnaea (Linn.). Not common Sphaerium rifico/a (Leach). River Welland — (orneum (Linn.). Caldecott, Edith Weston, Stockerston Brook — lacustre Qs/liiW.). A few in a pond near Caldecott Pifidium amnicum (Milll.). Not uncommon in small streams — casertanum (?o')_=: fontiiiale,?i.:iC'i. Not un- common in small streams — pusilkm (Gmel.) _ = font'male, auct.]. Not un- common in small streams — obtusalt, Pfr. Preston Brook — gassieiianum, Dupuy. Not uncommon in small streams (The correct determination of the species of Pisidium is open to question.) 37