816 MARINE SHELLS 



2. S. * centralis. Shell transversely oblong-oval, 

 slightly wrinkled concentrically, compressed, fragile, 

 rounded at each end ; hinge central, teeth two in the 

 left valve and one in the right ; epidermis pale yel- 

 io wish-brown ; a broad obsoletely elevated line 

 within, passes from the hinge towards the base, and 

 terminates beyond the middle. 



Length half an inch. 



Breadth one inch and three-tenths. 



Inhabits the southern shores. 



Cabinet of the Academy and Philadelphia Mu- 

 seum. 



Somewhat rare. It has very much the appearance, 

 at fivst sight, of the young of S. carabceus, but it can- 

 not be mistaken for it, as the teeth of the hinge are 

 invariably central, whilst those of that species are 

 anterior to the centre, and the interior of the shell of 

 that species has never the slightest appearance of a 

 costa. 



3. S. *viridis. Shell fragile, elongated, com- 

 pressed, a little narrowed before, slightly wrinkled 

 concentrically, the wrinkles regularly rounded to- 

 wards the extremity ; hinge margin nearly recti- 

 linear ; basal margin a little arquated ; anterior tip 

 rounded ; posterior tip obliquely truncated, a little 

 reflected, and rounded near the base ; hinge terminal; 

 teeth one in each valve, each having a flattened ver- 

 tical surface, which turns upon that of the opposite 

 tooth ; epidermis pale green. 



Length nine- twentieths of an inch, nearly. 



