Pvn H,i I'UitlS

298 CYPRINID.E.
Genus I. ISOCAE/DIA * Lamarck. PL 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 posterior
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 equivalve 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 f, Linne.
Chama Cor, Linn. Svst. Nat. p. 1137. I. cor, F. &H. i. p. 472, pi. xxxi\ .
f. 2 , and (animal) pi. N. f. G.
Body soft, yellowish - white : mantle completely lining the
shell ; margin of an orange
colour : tubes rather wide at their
* From its resemblance to a heart with equal sides. t Heart.