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rows; a slight and broad depression from the beaks 
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. 
OBSERVATIONS. 
A species allied to U. torsns, Raf. but very dis- 
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. un- 
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 CiELATUS. 
Plate III. — Fig . 4 . 
DESCRIPTION. 
Shell sub triangular, 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 
