56 



Bryant Walkkk 

 Genus STROPHITUS Rafinesque, 1820. 



Shell elliptical to rhomboid, inflated, subsolid, pointed or biangulate be- 

 hind, with a low posterior ridge, which is sometimes double; beaks full, 

 sculpture consisting of a fe\v, strong, concentric ridges, which curve sharply 



Fi^. 168 



Fig. 169 



upwards behind ; epidermis rayed or rayless, shining ; hinge line incurved 

 in front of the beaks; teeth rudimentary, a vestigial, compressed tooth in 

 each valve, and sometimes a secondary tooth ; laterals rarely present. Mar- 

 supium occupying the whole of the outer gills, consisting of short, hori- 

 zontal ovisacs, which run directly across the gills. 



Type: Anodonta iiudiilata vSay. 



Fxample: S. cdcntnhis (Say), fig. 168. Animal, fig. 169. 



Genus ANODONTA Lamarck, 1799. 



Shell elliptical, thin, inflated, often slightly winged posteriorly; beak 

 sculpture consisting of rather numerous, more or less parallel ridges, usually 

 somewhat doubly looped and becoming slightly nodulous on the loops ; sur- 

 face generally smooth, shining; hinge edentulous, reduced to a mere line, 

 regularly curved ; nacre dull. 



