AND DESCRIPTIONS OF NEW SPECIES. 113 



Hab. Ohio river, T. G. Lea. 



My Cabinet. 

 Cabinet of Professor Vanuxem. 

 Cabinet of P. H. Nicklin. 

 Cabinet of the Academy of Natural Sciences. 

 Cabinet of the American Philosophical Society. 

 Diam. 1*5, Length 1-9, Breadth 2-6 inches. 



Shell ovate, oblique, inequilateral, having an irregular nodulous line 

 near the middle passing obliquely from the beaks to the basal margin; 

 substance of the shell thick ; umbonial slope irregularly wrinkled ; an- 

 terior to the umbonial slope is a wide slightly impressed furrow; 

 beaks prominent, rounded, and situated near the anterior margin ; liga- 

 ment slender and somewhat long ; epidermis smooth, shining, yellow- 

 ish, with numerous small green rays which thickly cover the whole 

 disk except a small portion of the anterior part ; cardinal teeth rather 

 small, deeply cleft in the left valve, single and emerging from a pit in 

 the right valve ; lateral teeth long, nearly straight, and slightly en- 

 larged near the posterior end ; anterior cicatrices distinct ; posterior 

 cicatrices confluent; dorsal cicatrices situated on the under part of the 

 cardinal tooth ; cavity of the beaks wide and rounded ; nacre milk 

 white, rarely rose coloured. 



Remarks. — This extraordinary and highly interesting shell formed 

 one of the three divisions into which I had, in my cabinet, separated 

 the U. cornutus (Barnes). The other division has been called by 

 I)r Hildreth foliatus. Having, since the publication of my last 

 memoir*, received numerous young and perfect specimens, I have 

 concluded that the study of this group would be facilitated by its sepa- 

 ration into three species, which will stand thus ; U. cornutus (Barnes), 

 possessing three or four distinct horns between the beaks and basal 

 margin ; U. foliatus (Hildreth), having no elevation, but possessed of 

 two elongations, one at the basal margin, the other at posterior margin; 

 and U.perplexus (Nob.), possessed of an irregular oblique nodulous ridge 



* See note, Vol. \\\. p. 418. 



Vol. IV.— 2 D 



