278 AMERICAN JOURNAL 



DESCRIPTIONS OF AND REFERENCES TO MIOCENE 

 SHELLS OF THE ATLANTIC SLOPE, AND DESCRIPTIONS 

 OF TWO NEW SUPPOSED CRETACEOUS SPECIES. 



BY T. A. CONRAD. 



VENERID^E. 



MERCENARIA, Schum. 



M. percrassa, Conrad. PI. 19, fig. 1. — Araer. Journ. Conch., 



vol. Ill, p. 13, 1867. 

 M. cuneata. PI. 20, fig. 1. 



Description. — Subtriangular, ventricose medially, slightly 

 flattened or contracted above the umbo ; outline of the disk 

 nearly straight below the middle ; surface with coarse concentric 

 lines ; posterior side cuneiform, lower half of posterior margin 

 nearly rectilinear, extremity subacute ; inner margin minutely 

 crenulated. 



Locality. — Charles Co., Maryland. Prof. Cope. 



Remarks. — This species may be distinguished from M. merce- 

 naria in being less oblique, proportionally shorter and more 

 acute at the posterior extremity, and in having a more elongated 

 anterior cardinal tooth. 



CALLISTA, H. and A. Adams (not Poli.) 

 C. DENSATA. PI. 19, fig. 2. 



Description. — Ovate-triangular, inequilateral, subcompressed, 

 substance thick ; posterior side flattened and cuneate, acutely 

 rounded at the extremity ; surface polished ; lunule lanceolate ; 

 anterior cardinal tooth thick. 



Locality — Petersburg, Virginia. 



Dione densata, Conrad. — Proceed. Acad. Nat. Sciences, Vol. 

 XIV, (1862) p. 586. Thicker than D. albaria, Say, with a less 

 concave lunule margin and otherwise very distinct. 



CARYATIS, Roemer. 

 C. plionema, Conrad. PI. 20, fig. 3. 



Description. — Triangular, oblique, ventricose, inequilateral ; 

 moderately thick in substance ; anterior margin oblique, straight, 



