29 



rows; a slight and broad depression from the beukn 

 to the base; beaks and umbones very prominent; um- 

 bonial slope subangulated, submarginal; anterior 

 side short, subtruncated, posterior side flattened be- 

 hind the umbonial slope; epidermis rugose, olivace- 

 ous, with green interrupted rays, some of them 

 broad; cardinal and lateral teeth much elevated, 

 granulated and sulcated; anterior and posterior mus- 

 cular impressions profound; nacre white; iridescent 

 on the base. 



OESERVATIOxNS. 



A species allied to U. iorsus, Raf. but very di?:- 

 tinct; it is broader and more cordate than any of the 

 kindred species with which I am acquainted. Young 

 specimens have an outline much resembling U. wi- 

 datus, of Barnes; but mature individuals are slight- 

 ly produced and cuneiform on the posterior end, like 

 some varieties of U. triangularis, of Raf.; young 

 shells are beautifully rayed. 



Inhabits Elk and Flint rivers, Alabama. 

 UN 10 C^LATUS. 

 Plate III.— Fig. 4. 



DESCRIPTION. 



Shell subtriangular, very inequilateral, much com- 

 pressed; with a broad furrow extending from the 

 beaks to the base; anterior side and umbo entire, and 

 the remaining parts furnished with small irregular 

 c 2 



