KENNAED & WOODWAKD : ON PLEISTOCENE MOLLUSCA. 357 



Moreover, in the Holocene, Planorhis Stroenni is a noteworthy 

 member of the same group. All these forms are only known fossil 

 in these Islands fi-om the Thames-Rhine system of deposits. 



Vino littoralis, which first occurs fossil in the 100 feet terrace of 

 the Thames at Swanscomb, and Paludestrina marginata, the first 

 appearance of which in these Islands is in the Cromerian (Forest Bed 

 of Norfolk and Suifolk), possibly reached England by two routes : one 

 by means of the Ehine and Thames, whilst the other, since they 

 occur in the Pleistocene of Cropthorne, in the Severn River system, 

 was by way of the western rivers of France and the Severn, for the 

 connection between the upper waters of the Severn and the Thames 

 must have been severed for a long period when the Cropthorne Bed 

 was deposited. The occurrence of Corhicula flwninalis, Paludestrina 

 confusa, and Planorhis vorticulus at West Wittering furnishes 

 additional proof that the rivers of Sussex were at one time connected 

 with the Thames-Rhine system. 



There is one living English species which is a well-marked member 

 of this group, Assemama Grayana, known only from Denmark, 

 Belgium, and the Thames Estuary, but as yet it is unknown in 

 a fossil state, although the name has figured in some lists. 



