﻿UNITED STATES. 53 



cally undulate at the beaks; epidermis yellowish, polished ; cardinal teeth compressed, 

 crenulate ; lateral teeth long, lamellar and much curved ; nacre white and iridescent. 

 Proc. Acad. Nat. Sci., 1857, p. .84. 



Hah. — Jackson, Mississippi. U. P. James. 



Cabinet of Mr. James, Cincinnati. 

 Diam. '8, Length 1-5, Breadth 28 inches- 



Shell smooth, elliptical, compressed, very inequilateral, very much compressed be- 

 hind, rounded before, emarginate at base ; substance of the shell rather thick, thinner 

 behind ; beaks a little prominent, rather small, with 7 or 8 small, concentric folds on 

 the apex ; ligament very long and thin ; epidermis yellow, inclining to brown, smooth, 

 polished, with rather distant marks of growth ; near the margin quite yellow ; poste- 

 terior slope elevated into a keel, and furnished with two impressed lines on each 

 valve from the beaks to the posterior margin ; umbonial slope rounded ; cardinal teeth 

 compressed, crenulate and rather stout; lateral teeth long, lamellar, very much and 

 regularly curved ; anterior cicatrices distinct ; posterior cicatrices confluent ; dorsal 

 cicatrices placed near the centre of the cavity of the beaks ; cavity of the shell very 

 shallow ; cavity of the beaks shallow and sub-angular. 



Remarks. — A single specimen of this species was submitted tome by Mr. U. P. James, 

 of Cincinnati, and to him I dedicate it. It belongs to that group of which U. camp- 

 todan, Say, may be considered the type. It may be distinguished by being more ellip- 

 tical, in being higher on the posterior slope, and the lateral teeth are longer and more 

 curved. It is closely allied to U. rnanubius, Gould, but is more elliptical, smoother, 

 more compressed, and less angular behind, the lamellar teeth being shorter and more 

 curved. 



The lateral teeth are very remarkable for their length and their being much curved, 

 the plate on the dorsal arch not being simply rounded. The cicatrix of the anterior ad- 

 ductor muscle is unusually large. Some of the lines of growth are marked by a yel- 

 low band. 



Unio subgibbosus. PL 6, fig. 36. 



Testa laevi, elliptic^, compressa, valde inrequilaterali, postice subangulata, valvulis crassis, planulatis ; nati- 

 bus vix prominentibus ; epidermide tenebroso-olivaeea, striata, obsolete radiata ; dentibus cardinalibus, 

 parvis, brevibus crassisque ; lateralibus longis, crassis curvisque ; margarita vel alba vel salmouis co- 

 lore tincta. 



Shell smooth, elliptical, compressed, very inequilateral, subangular behind ; valves 

 thick, flattened; beaks slightly prominent ; epidermis dark olive; striate, obsoletely 

 rayed; cardinal teeth, small, short and thick; lateral teeth long, thick and curved; 

 nacre white or purple. 



Proc. Acad. Nat. Sci. 1857, p. 1G9. 



14 



