CYTHEREA. 131 



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

 coast except Venus mercenaria, with which it was confninded by 

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

 also l)y wanting the j>urple border along the interior margin of the 

 shell. 



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

 series 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 the wrinkles, Ijeing much 

 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 lena'th. 



'&' 



Family VENERIDiE. 



Shell equivalve, triangular, rhomboidal, or globular ; 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 with three or four cardinal teeth- 

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

 of which are cloven or do^lble, and an obscure and ridge-like lateral 

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

 scars oval and distinct. 



Ocnus CYTHJEREA, Lamarck. 1805. 



Shell inequipartite, 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, fi<^. 3; vi. 261. — 

 SowERisy, Thes. Conch. (Cyth.) 6.38, pi. 132, tig. 119. — De Kay, Nat. Hist. New 

 Yoi-k, 216, 1)1. 27, fio:. 279. — Han-ley, in Wood's Index, Suppl. pi. 15, fig. 34.— 

 RoMKH, Maine Rlntt. ix. 68. 



