1849.] 



153 



extremity very thin and fragile ; anteriorly regularly rounded ; posteriorly some- 

 what pointed, with an acutely rounded extremity; basal margin regularly curved ; 

 summits prominent, eroded ; posterior margin very oblique and nearly straight ; 

 epidermis ochraceous and olivaceous; rays green, not very distinct on the 

 middle and anterior side, but more so posteriorly, some rather broad, others 

 linear ; posterior slope dark coloured, rayed ; within white and highly iridescent 

 posteriorly; cardinal teeth much compressed and oblique, double in each valve; 

 lateral teeth very slightly curved, finely granulated. Sj. 



Inhabits mill ponds ; Ogeechee River, Georgia. 



U. Ogeecheensis. Elliptical, thin, inflated ; posterior side somewhat pointed, 

 extremity subangular ; valves slightly contracted from beak to base; summits 

 rather prominent, decorticated, slightly undulated; epidermis ochraceous with 

 interrupted green rays, some of them broad ; within white, highly iridescent 

 posteriorly; cardinal teeth oblique, compressed; lateral teeth rectilinear. 3. 



Inhabits Ogeechee River, Georgia. 



Allied to the preceding, but has a lighter coloured epidermis with more distinct 

 rays, is proportionally longer; the cardinal tooth in the left valve is longer and 

 less lobed, and the lateral teeth are straight, without granules, and less oblique 

 than in the preceding species, which is a larger shell. 



U. oratus. Widely elliptical, ventricose, gaping at both ends; posterior gape 

 wide; anterior extremity rather acutely rounded; posterior margin sinuous, 

 extremity subangular ; basal margin forming a nearly regular curve ; summits 

 prominent; umbo and beak eroded; epidermis ochraceous, polished; cardinal 

 teeth compressed, oblique ; lateral teeth straight ; within white, inuch stained 

 with waxen yellow. Z\. 



Inhabits Flint River, Georgia. 



This shell has the polished epidermis of U. cariosus, but is without a ray. It 

 is longer in proportion than that species with very different cardinal teeth, which 

 are much nearer parallel with the margin above : the shell also gapes far wider 

 in the only specimen I have seen. 



U. rosaeeus. Widely elliptical, ventricose above; posterior margin obliquely 

 truncated, slightly sinuous; extremity subangular or acutely rounded ; epidermis 

 ochraceous and dark brown ; rays indistinct, frequently broad, but composed of 

 fasciculi of lines; surface with fine radiating wrinkles ; within deep rose-purple; 

 cardinal teeth prominent, oblique, compressed, trifid or 3 teeth in the left 

 valve. 3i. 



Inhabits Savannah River. 



Allied to U. ochraceus. Say. 



U. eontrarius. Elliptical, moderately thick; valves somewhat flattened or 

 plano-convex ; umbo and beak not prominent, much eroded ; umbonial slope 

 acutely rounded; posterior margin straight above, truncated, direct; epidermis 

 deep ochraceous, with linear radiating wrinkles, and obscurely rayed about the 

 umbo; within pale flesh-colour stained with waxen yellow ; cardinal teeth direct, 

 thick, sulcated, not very prominent ; lateral teeth reversed, or the double tooth 

 in the right valve. 3 1-5. 



Inhabits the Ogeechee River. 



22 



