44 



nent, not nearly terminal; posterior margin obliquely 

 truncated; umbonial slope rounded; base arcuated; 

 epidermis olivaceous, obscurely rayed, wrinkled on 

 the margins; cardinal and lateral teeth very promi- 

 nent, granulated; nacre whitish and iridescent on 

 the posterior margin. 



Variety A. Epidermis reddish brown; nacre rose 

 coloured. 



OBSERVATIONS. 



I found a very few specimens of this shell at Clai- 

 borne, on the Alabama river; it is allied to U. multi- 

 radiatus, Lea, but on comparing it with specimens 

 of that species in Mr. Poulson's cabinet, I found it 

 sufficiently distinct; the nacre is denser, and thicken- 

 ed on the margin; and the rays are of nearly uniform 

 size, distant and obscure. The lateral teeth closely 

 resemble those of U. multiradiatus. 



UNIO PRASINUS. 

 Plate III.— M^. 1. 



DESCRIPTION. 



Shell suborbicular, compressed, with distant con- 

 centric impressed lines; anterior margin obtusely 

 rounded; posterior margin wide, truncated, not 

 oblique; basal margin straight, parallel with the liga- 

 ment margin; beaks prominent; epidermis olive yel- 



