124 The Mollusca of Cambridgeshire 



Cambridgeshire is too scanty to risk any comparison in detail 

 between it and that of the higher land round and to the south 

 of the county town. 



In the above mention of the forms likely to be met with 

 in different directions varieties have been neglected. An 

 attempt to deal with these would prolong this account unduly, 

 and also the very unequal values attaching to the varieties 

 which have received names more or less recognised render 

 it inadvisable to lay any stress upon them without at the 

 same time weighing individual claims. Hence, in what has 

 already been said, and in the remainder of this account, 

 varieties of species are referred to only in a few necessary 

 cases. 



The following is a list of species which have been obtained 

 in the living state in the county, the figures placed after the 

 names indicating occurrence in the local Pleistocene deposits, 

 as follows: (1) Marine-shell-bearing gravels of the March 

 district; (2) Gravels of the ancient river system of the Cam- 

 bridge district; (3) Gravels of the present river system as 

 exposed at Barrington, Barnwell, Grantchester, &c. ; (4) Fen 

 silt; (5) Shell marl, as at Burwell, Stretham, Soham, Laken- 

 heath, and between Littleport and Downham in Norfolk. 



GASTEROPODA. 



STREPTONEURA 



ASPIDOBRANCHIATA 

 RHIPJDOGLOSSA 

 NERITIDAE 



Neritina (Theodoxia) fluviatilis (Linn.) 

 PECTINIBRANCHIATA 

 TAENIOGLOSSA 

 POMATIIDAE 



Pomatias elegans (Mull.) (3) 



