SvNorsis Frksh-Water Mollusca 



71 



post-base ; beaks compressed, sculpture unknown ; epidermis brownish, 

 cloth-like ; pseudo-cardinals divided into irregularly radiating, granular lam- 

 ina, sometimes to the number of a dozen or more in each valve ; hinge-plate 

 reduced to a mere rounded line behind the pseudo-cardinals ; laterals short, 

 remote. Ovisacs apparently separated from each other by a sulcus. 



Tvpe : Unio rotiindata Lam., fig. 199. 



Genus TROPTERA Rafinesque, 1819. 



Fig. 200 



Shell usually large, gaping at anterior edge and edge of dorsal slope, 

 winged along the dorsal region when young and often when adult ; beak 



