MARINE MOLLUSCA OF THE UNITED STATES. 161 



3. C. TRIDENTATA, Say. Figs. 424, 425. 



{Venericardia.) Journ. Philad. Acad., v. 216, Am. Conch, t. 40. 

 Shell suborbicular, subequilateral, thick and ponderous, with 

 about eighteen convex ribs, crossed by concentric elevated lines ; 

 within the margin is deeply crenate; hinge with two diverging 

 teeth, separated by a large cavity in one valve, and in the other 

 a single, large, triangular, recurved tooth, closing into the cavit}-. 



Length G.5, height 6 mill. 



South Cdrolina. 



This is a somewhat doubtful species, and appears to have been 



described from a single specimen, which was possibly 3'oung and 



the hinge not perfect. Can it be the young of C. Novanglice? 



Conrad has made a genus " Pleuromeris^^ for his G. tridentata^ a 



fossil shell which is not specifically identical with Say's species, 



although it belongs apparently to the same group. 



Spurious and Doubtful Species. 

 C. INCRASSATA, Sowb., Conrad, Mar. Conch., is an East Indian 



species. 

 C. (Carditamera) Floridana, Conrad, Fossil Shells, 12. 1837. 



Inhabits Key West and Tampa Bay, Florida, but I think it has 

 not been detected on the Atlantic coast, although it is included in 

 Stimpson's Catalogue. 



Venericardia cribraria. Say, cover of Am. Conch., pt. 5. 



A single specimen from the coast of Xew Jerse3^ Say writes 

 " can this be a A^ariety of the borealU of Conrad ? Having but a . 

 single specimen, I cannot determine] this question." 



Family LUCmiD^. 



Animal with mantle-lobes open below, and having one or two 

 siphonal orifices behind ; foot elongated, cylindrical, or ligulate, 

 protruded at the base of the shell; gills one (or two) on each side, 

 large and thick, oval; mouth and palpi usually minute. 



The Lucinidai are distributed chiefly in the tropical and tem- 

 perate seas, upon sandy and muddy bottoms, from the sea-shore 

 to the greatest habitable depths. 



Syiiopsis of Genera. 

 Shell orbicular, white ; umbones depressed ; Innule distinct ; margins smooth 

 or minutely crenulated ; ligament oblique, semi-internal ; hinge teeth 3.3, 

 laterals 1-1 and 3-3, or obsolete; muscular impressions rugose, anterior 



