294 [Oct. 1847. 



trie lines, and a few larger impressed lines ; posterior margin truncated, direct ; 

 anterior end and anterior basil margins regularly rounded ; posterior basal 

 margin obliquely truncated ; beaks nearest the posterior end. Length 6-10. 

 Height 6-10 nearly. 



Corbula intastriata. 



Subtriangular, inflated, rostrated posteriorly ; within with fine radiating lines ; 

 Length . Very rare. 



1. Corbula alta. 



Subtriangular, profoundly elevated, slightly oblique ; larger valve ventri- 

 cose ; summit very prominent ; umbo broad ; hinge plate thick, with large 

 teeth ; smaller valve somewhat flattened, angular over the umbonial slope. 

 Length 6-10 nearly. Height 6-10. 



Occurs abundantly about 8 miles N. E. of Vicksburg, and always water- 

 worn. 



2. Corbula engonata. 



Triangular, inequilateral, small; valves nearly or quite equally convex, and 

 with angular concentric ridges ; posterior slope concave ; umbonial slope cari- 

 nated. Length 3-10. 



Chama Mississippiensis. 



Suboval, irregular, adhering; larger valve ventricose, with numerous irregu- 

 lar radiating lines, squamose inferiorly ; upper valve with numerous concen- 

 tric lines, with numerous small scales. Length f. Height 6-10. 



Rare, and occurs on Dr. Smith's plantation, 6 miles N. E. of Vicksburg. 



Pectunculus arctatus. 



Short-ovate, convex depressed, with little prominent flattened radii, divided 

 by a longitudinal impressed line towards the base ; anterior margin truncated : 

 posterior margin nearly rectilinear. Length . Height 6-10. 



Rare, and occurs on the bank of Yazoo river, about 14 miles from Vicksburg. 



There is in the collection a valve of another species of Pectunculus, which 

 is small, and resembles the young of P. pulvinatus. 



1. Nucula serica. 



Subelliptical, with minute regular concentric closely-arranged lines ; ante- 

 rior end acutely angular ; posterior end acutely rounded ; posterior side 

 shortest. Length . Common. 



2. Nucula Vicksburgensis. 



Obliquely subtriangular, convex, with minute obsolete radiating lines about 

 the base ; lunule elliptical, very large and impressed. Length ^. Rare. 



Area Mississippiensis. 



A species of Area occurs in great abundance at Vicksburg, which Lesueur 

 obtained many years since and named it, but I have forgotten the name, and 

 know not whether he published it in Europe or not. It is rhomboidal, ventri- 

 cose, with rather distant ribs in the right valve, slightly grooved in the middle ; 

 in the left valve ribs double and granulated ; inner margin profoundly toothed. 

 Length 8-10. 



