33 



the anterior muscular impressions are confluent, and 

 the posterior impressions distinct. 



Not uncommon in the head waters of the Black 

 Warrior river. 



I hav^e given this species the name of my friend, 

 .Tacob Green, M. D., Professor of Chemistry in 

 Jelierson College, a gentleman Avell known as a 

 contributor to the science of Conchology. 



UNIO PENITUS. 



Plate Y.—Fig. 1. 



DESCRIPTION. 



Shell triangular, very thick, except on the posterior 

 side, v^entricose; umbones flattened; beaks prominent 

 and rounded; umbonial slope angulated; posterior 

 margin flattened; a broad convex elevation com- 

 mencing near the base and projecting on the poste- 

 rior extremity, with radiating prominent lines, which 

 dentate the margin, and concentric grooves; epider- 

 mis olivaceous, wrinkled; ligament very short; car- 

 dinal teeth double in both valves, thick, prominent, 

 sulcated and granulated; posterior muscular impres- 

 sion very large and deep; nacre very white; irides- 

 cent in the cavity of the umbonial elevation; cavity 

 capacious. 



OBSERVATIONS. 



This shell has much the form of U. Iriqueter cC 



