CONCHIFERA. 



223 



or less orbicular, and convex ; ligament marginal, three or 

 four small acuminated teeth about the hinge: the line of 

 attachment of the mantle has a deep sinus extending 

 nearly to the beak ; muscular impressions rounded, small, 

 distant from the hinge, ligament external.* — (Fossil.) 



Cyprina. Lam. — Shell rather orbicular, equivalve, 

 inequilateral, obliquely heart-shaped, covered with a thick 

 brown epidermis ; ligament 

 large external, three cardi- 

 nal teeth, and generally one 

 lateral tooth in each valve ; 

 bosses turned on one side, 

 no lunule, and no sinus in 

 the pallial impression. 

 Animal, suborbicular ; the 

 mantle freely open with 

 plain or serrated edges: 

 siphonal orifices sessile or 

 nearly so, their margins fringed, the branchial the largest ; 

 foot large, linguiform ; labial palpi moderately long, trian- 

 gular.f — 1 species ; also fossil. 



C. Islandica, which is found in the Northern Seas, 

 and on our own shores, often attains a large size, and is 

 covered with a brown epidermis. 



Donax. Lin. — Shell, equivalve, inequilateral, trans- 

 verse, wedge-shaped, cardinal teeth 

 two on one or both valves, lateral, 

 variable, ligament on the shortest 

 side, which is often very much flat- 

 tened and truncated ; valves more or 

 less crenulated at the margin; the 

 pallial sinus wide and deep : an epi- 

 dermis. Animal oblong, its mantle Donax - 



* Sow., Conch. Manual. f Forbes's British Moll. 



Cyprina Islandica. 



