39 
not consider it a variety of any hitherto described. 
The figure represents one of the largest specimens 
which I found. 
UNIO FURVUS. 
Plate YI. — Fig. 3 
DESCRIPTION. 
Shell oval, ventricose, thick before, thinner behind, 
posterior margin wide, hardly angulated; umbonial 
slope angulated, behind which is an obscure impress- 
ed line; epidermis almost black, with minute crowded 
wrinkles; cardinal teeth slightly oblique, pyramidal; 
within white, highly iridescent on the posterior 
margin. 
O B S ERV ATI O N S. 
A species which I found in the Black Warrior 
river, in company with the preceding; it is very rare. 
UNIO RAVENELI. 
Plate VI. — Fig. 4. 
DESCRIPTION. 
Shell oblong oval; ventricose; beaks hardly promi- 
nent; ligament margin straight, not oblique; base 
very slightly arcuated; umbonial slope angulated, 
