CYTHEREA. 131 



It is one of our largest shells, and resembles no other shell of our 

 coast except Venus mercenaria, with which it was confounded by 

 Pennant. From this it is easily distinguished by its epidermis, and 

 also by wanting the purple border along the interior margin of the 

 shell. 



It is subject to very little variety. Sometimes the surface has a 

 scries of concentric ridges, and sometimes the beaks are unnaturally 

 elevated and curved. Old shells have a very dark epidermis, and 

 are generally much decorticated. The young are of a light fawn- 

 color, with darker and lighter zones, and tlie wrinkles, being nnicli 

 raised and very regular, give the surface a very pretty appearance. 

 The rougher surface, greater proportionate length, rounded form, 

 and want of a lunule, distinguish them from Astarte quadrans, of a 

 similar size. From Astarte elliptica they differ little, externally. 



They are obtained of every size, from one fourth of an inch to four 

 inches in length. 



Family YENERID.E. 



Shell equivalve, triangular, rhomboidal, or gloliular ; variously 

 sculptured or almost smooth ; beaks incurved, and turned towards 

 the anterior side ; ligament external, placed on the larger side of 

 the shell ; hinge strong, furnished Avith three or four cardinal teeth 

 in each valve (one genus having two only in the left valve), some 

 of which arc cloven or doultle, and an obscure and ridge-like lateral 

 tooth on the posterior side ; pallial scar deeply sinuous ; muscular 

 scars oval and distinct. 



Oeiitis CYTHEREA, Lamarck. 1805. 



Shell incquipartite, rounded ; hinge with four diverging teeth in 

 one valve, one of which is separate from the others, and three in 

 the other valve ; no lateral teeth. 



Cytherea convexa. 



Fig. 49. 



Shell oval, tumid ; lunule heart-shaped ; beaks prominent and recurved ; color 

 chalky Avhite. 



Cytherea convexa, Say, Journ. Acad. Nat. Sc. iv. 149 (1824), pi. 12, fig. 3; vi. 261. — 

 SowERHY, Thes. Conch. (Cyth.) 638, pi. 132, fitr. 119. -De Kay, Nat. Hist. New 

 York, 216, pi. 27, fiij. 279. — Hanley, in Wood's Index, Suppl. pi. 15, fig. 34.— 

 RoMEK, Malac. Blatt. ix. 68. 



