298 CYPRINIM. 



Genus I. ISOCARDIA * Lamarck. PI. VI. f. 1. 



Body globose, small in proportion to the shell : mantle thin ; 

 edge double, but plain : tubes sessile ; orifices papuliferous : 

 foot broad,, compressed, and triangular. 



Shell heart-shaped when viewed sideways, smooth or con- 

 centrically striated : epidermis longitudinally ciliated : beaks 

 separate, and involute or spirally twisted : lunule incomplete : 

 corselet none : ligament wholly external, forked outwards on 

 the anterior side, owing to the divergence of the beaks : teeth, 

 in each valve two cardinals, placed obliquely, the outer one 

 being laminar and curved, besides a single lateral on the pos- 

 terior side. 



The only species which we possess of this eccentric 

 genus was placed by Linne in Chama, and by Bruguiere 

 in Cardita ; Lamarck properly separated it from both, 

 and it constitutes the type of his Isocardia. It may 

 be known from Cardita by its convolute and twisted 

 beaks, and from Chama by being both equi valve and free. 

 Lamarck placed it at the end of the "Cardiacees," on 

 account of its general resemblance to the Cockles. The 

 globular and cordate form of the shell is very elegant. 

 Carpenter says that the external layer has scarcely a 

 vestige of the tubular structure which is so conspicuous 

 in Cardium. The epidermis of the European Isocardia 

 is much thicker than that of tropical species of the same 

 genus. No species appears to have been found on the 

 northern coasts of America. Poli called the animal 

 Glossus. 



Isocardia cor-}-, Linne. 



Chama Cor, Linn. Syst. Nat. p. 1137- /. cor, F. &H. i. p. 472, pi. xxxiv. 

 f. 2 , and (animal) pi. N. f. 6. 



Body soft, yellowish - white : mantle completely lining the 

 tell ; margin of an orange colour : tubes rather wide at their 



* From its resemblance to a heart with equal sides. t Heart. 



