Fossil and Recent Shells. 341 



CORBULA. 



1. C. idonea. Shell subtrlangnlar, convex, thick, obscurely un- 

 dulated ; with a fold on the posterior sub-margin and the extremity 

 angular; basal margin acute; cardinal tooth very thick and elevated. 

 Length, one inch. 



Locality. — Choptank river near Easton, Md., common ; Upper 

 marine. 



2. C. oniscvs. Shell elevated ; larger valve ventricose, with pro- 

 found sulci terminating at the umbonial slope, which is carinated ; 

 posterior extremity narrowed and truncated., from the posterior angle 

 of which a carina extends to the apex, nearly parallel with that of 

 the umbonial slope; superior valve concentrically striated. Length, 

 one third of an inch. 



Locality. — Claiborne, Alab. London clay. 



This species can hardly be distinguished from the C. angustata of 

 Sowerby, Geological Trans. 2d series, vol. iii, pi. 38, fig. 4. The 

 latter was found in the valley of Gosau, Saltzburg Alps. 



CHAMA. 



1. C. congj-egata. Shell sessile, dextral; superior valve a little 

 convex, with numerous erect elevated arched scales ; beaks occa- 

 sionally rostrated ; apex sub-spiral ; scales on the inferior valve 

 broader and more elevated ; inner margin crenulated. 



Locality. — James river, near Smithfield, Va. Upper marine. 



2. C. corticosa. Shell sinistral; with strong concentric undulated 

 laminae transversely striated ; superior valve flat; inner margin cren- 

 ulated. Found with the preceding species. 



PETRICOLA. 



P. centenaria. Shell oblong oval, with numerous prominent ra- 

 diating striae, and concentric wrinkles ; lunule small, cordate, pro- 

 foundly impressed ; hinge with two teeth in one valve, and three in 

 the opposite, the middle one bifid. Length, two inches. 



Localities. — James river near Smithfield, Va.; Choptank river 

 near Easton, Md. Upper marine. 



PECTEN. 



P. ehoreus. Shell suborbicular, compressed, thin, a litde oblique; 

 ribs about twenty two, rounded, litde elevated and smooth ; inferior 

 valve nearly flat. Length, two inches. 



Locality. — Suflx)lk, Va. Upper marine. 



