32 



pyramidal; nacre bluish white and iridescent poste- 

 riorly; cavity capacious; most so under the umbonial 

 slope. 



OBSERVATIONS. 



A species distantly allied to U. iris, Lea, but dif- 

 fering in its greater convexity and elevation, as well 

 as in the peculiarity of its rays, which disappear on 

 the anterior side; an impressed line is visible in some 

 specimens, on the posterior submargin. I found 

 several in the Black Warrior river, south of Blount's 

 Springs, Alabama. 



UNIOGREENII. 



Plate W.—Fig. 1. 



DESCRIPTION. 



Shell subovate, thick before, thinner behind; an- 

 terior side not very short, rounded, beaks slightly 

 prominent; umbonial slope straight, subangulated; 

 epidermis wrinkled, olivaceous, rayed only on the 

 posterior side; cardinal teeth thick; lateral teeth 

 striated and minutely granulated; within bluish 

 white, iridescent on the posterior margin; a short 

 obtuse elevation passing obliquely from beneath the 

 cardinal teeth; cavity moderately capacious. 



OBSERVATIONS. 



A species which cannot be confounded by an accu- 

 rate observer Avith any other heretofore described; 



