KENNAED & WOODWARD : OS SPECIES OF VIVIPARA. 67 



examples are the largest we have seen, specimens from this locality 

 attaining 27 mm. in altitude, with a maximum breadth of 19*5, the 

 largest Clacton specimen noted being 25 by 19 mm. Up to the 

 present this shell is only known in this country from Clacton and 

 Swanscomb, and additional evidence is thus afforded of the importance 

 of the old Thames-Rhine river system in the distribution of fresh- water 

 moUusca. 



