65 



primary teeth very small, almost obsolete, sometime* 

 two on each valve, of which one is plaited in the 

 middle on the one valve, and sometimes two plaited or 

 folded teeth on the other. These shells inhabit 

 fresh waters. 



Cyclas rivicola 



cornea 



lacustris 



- obliqua 



calyculata 



Cyclas obtusalis 



fontlnalis 



australis 



sulcata 



striatina 



Cyclas Sarratogea. 



CYRENA. 



TELLINA FLUMINEA, Gftielin, 



Sowerhys Genera No. 5, pi. 2. 

 These shells inhabit rapid rivers and streams, and 

 have been classed with the preceding genus, from 

 which they are however distinct, having three cardi- 

 nal teeth on each valve, and also lateral teeth. They 

 are thick, solid shells; sometimes of a great size : the 

 apices eroded or carious; covered on the other parts 

 with a green or brownish epidermis. Ligament exte- 

 rior, and placed on the largest side. 



