DIMYARIA. 143 



prominent; the internal margins of the valves denticulated 



or plicated; hinge with four teeth in both valves; the two 



primary approximate, mutually inserted and crossing each 



other; two lateral remote entering teeth. 



Section * Shells with no particular angle at the umbones, and the 

 anterior side at least as large as the posterior. ** With the umbones 

 caiinated or angulai', the posterior side often much larger than the 

 anterior. 



Cardium edule. — The Edible Cardium. Plate XVT. 

 fig. 14. With about twenty-six depressed ribs, and trans- 

 verse obsolete scales; outside yellowish- white, inside white; 

 beaks protuberant. One to one and a half inch long. In- 

 habits the European seas, and used as an article of food. 



TRIBE V. CONCIIACEA. 



With at least three primary teeth in one valve, and the 

 other generally the same, although sometimes with fewer. 



Section I Marine. 



Usually destitute of lateral teeth ; epidermis generally 

 wanting, or caducous. 



Genns 1 9— VENERIC AUDI A.— ZamarcA-. 



Generic Character — Equivalve, inequilateral, suborbicu- 

 lar; generally with longitudinal radiated ribs; hinge with 

 two oblique teeth in each valve, turned in the same direc- 

 tion. 



Venericardia imhricata. — The Imbricated Venericar- 

 DlA. Plate XVI. fig. 17. Suborbicular, having convex 

 longitudinal ribs, covered with imbricated, rough scales. 

 One and a half inch long. Fossil at Grignou. 



Genus 20.— ORTYGTA— /.f«cA. 



Generic Character. — Shell equivalve, transverse, three 

 primary teeth in each valve, two of which are approximate, 

 and the other remote; with the ligament subextenial ; um- 



