30 GENERA OF SHELLS. 



found in all seas, and generally live buried in the sand 

 near the coasts. 



(a.) JY0 particular angle on the beaks, and the anterior side 

 at least as large as th& posterior. 



C. costatum, Indicurn, ringens, Asiaticum, lenuicostatum, 

 fimbriatum, Brasilianum, apertum^ papyraceum, bullatum, 

 ciliare, echinatum, pseudolhna, aeuleatum, erinaceum, tuber- 

 culatum, isocardia, muricatum, angulatum, marmoreum, 

 elongatum, ventricosum, rugosum, sulcatum, serratum, laevi- 

 gatum, biradiatum, aBolicum, pectinatum, rusticum, edule, 

 Groenlandicum, latum, crenulatum, exiguum, rninutum, 

 roseum, scobinatum, Mortoni, pinnulatum. 

 (b.) Beaks carinated, or having an angle; posterior side 

 often larger than the anterior. 



C. unedo, medium, fragum, retusum, tumoriferurn, hemi- 

 cardium, cardissa, inversum, Junonias, lineatum. 



CARDITA. Shell, free, regular, equivalve, 

 inequilateral. Hinge with two unequal teeth ; 

 one short, straight, under the beaks, the other 

 oblique, marginal, prolonged under the corse- 

 let. 



The carditae may be easily confounded with the 

 venericardise, if sufficient attention be not paid to the 

 direction of the two teeth, which in the latter are both 

 oblique and turned to the same side, which is not the 

 case in cardita. They differ from chama in not being 

 inequivalve, or irregular, nor ever fixed by the lower 

 valve to marine substances. Some species are said to 

 fix themselves .by a sort of byssus, like the area and 

 mytilus. 



(a.) Shell subcordatc or oval, more transverse than longi- 

 tudinal. 



C. sulcata, ajar, turgida, squamosa, gallicana, intermedia, 

 rudista, Etrusca, tarpezia, bicolor, depressa. 



