150 TESTACEOUS MOLLUSCA. 
truncated and carinated with its slope more or less concave: teeth 
and anterior end often tinged with purple internally: anterior dorsal ~ 
edge rather incurved.—-Variety. C. Rosrrata. Lam.3. With 
the anterior side produced attenuated and slightly beaked. 12.— 
New Holland. ; 
C. CoratuiopHaca. Lam. 4.—Bl. t. 76. f.3.—CHama C. 
Gmel. 3305.—D. p. 220.—W. t. 9. f. 17.—Ch. f. 1673, 4. 
Oblong, rounded at both extremities, cylindraceous, thin, white 
tipped with purple at the beaks, diaphonous, compressed anteriorly ; 
marked with decussated striee which at the margin are raised into 
low ridges. 2.—In Madrepores at St. Domingo. (Bears some 
resemblance to Mytilus Lithophagus.) 
HIATELLA. 
Equivalve, very inequilateral and transverse ; gaping at the ventral 
margin ; hinge with a small tooth in the right valve; and two 
oblique somewhat larger ones in the left valve; ligament 
external, 
H. Arctica.* Lam.—Turt. Biv. t. 2. f. 12.—SoLten Minv- 
tus. Lin. 1115.—W. t.3. f. 33.—D. p. 69.—Mont. t. 1. f. 4. 
—Ch. f. 51, 2.—Saxtcava A. Phil. t.3.f.3. Oblong, produced 
and truncated anteriorly, white with transverse wrinkles, ligamental 
edge subincurved, anterior slope with two oblique ridges usually 
armed with spines.—Variety. Without the spines. (H. Os- 
tonca. Turt. Biv. t. 2. f. 13.) $.— Atlantic and Mediter- 
ranean.} 
ISOCARDIA. 
Equivalve, heart-shaped, ventricose ; beaks distant, divergent, and 
spirally turned to one side; hinge with two primary flattened 
tecth, one of them recurved and under the beak; an elongated 
lateral one under the ligament which is external and forked on 
one side. 
I. Cor.* Lam. 1.—Bl. t. 69. f. 2.—Cuama Cor. Lin. 
1137.—D. p. 212.—Ch. f. 483.—E, t. 232. f2 1.—Don. 4. 
t. 134.—W. t. 9. f. 1. Heart-shaped, globose, smooth, fulvous 
and the beaks clouded with white; epidermis reddish. 3..23.— 
Europe. 
I. Moutrniana. Lam. 3.—CuHama M. JD. p. 213.—Ch. 
Sf. 484, 5, 6, 7.—E. t. 233. f. 1—Carpira M. Brug. Dice. 
p. 404. Heart-shaped, subtriangular, inequilateral, yellowish white, 

' Compare Mytinus Pracisus of Montagu. t. 4. fi 2.—(W. 
¢. 12. f. 11.) 
