308 TESTACEOUS MOLLUSCA. 
more or less obtuse rib-like longitudinal folds, which are generally 
imbricated by foliaceous concentric lamelle (varying in closeness and 
elevation), and are rarely profound: inside centrally whitish, margin 
quite entire, often with a few minute denticles at the hinge: beaks 
not prominent. China ? 
O. Grauctna. Lam, 42. Oval or oval-oblong, tumid, with the back 
varying from purplish brown to tawny-purple, having a peculiar 
resinous lustre, with obtuse and transversely wrinkled folds: posterior 
side denticulated near the hinge.-—Var. Disk irregular, almost de- 
void of folds. 2%. Hab.? Certain large and strong specimens of 
Prrcata sufficiently agree with this description. 
O. Strensis. Gmel. 3335, and D. p. 275, from Ch. f. 668 (termed 
by Bolten O. Prw-Apamirica), copied E. t. 184, f.1, and W.t.11, 
f. 64.—Haml. Conch. Mis. Os. f. 9, 12.—O. Fusca, Lam. 43. Strong, 
more or less orbicular, of an uniform dull purple, with blunt radiating 
folds and concentric lamelle ; subequivalve, usually affixed by about 
half its lower surface, devoid of tubular processes of attachment. 
Inside whitish, except at the margin, which partakes of the external 
colouring, and is not at all scabrous, but displays some coarse raised 
wrinkles at the extremities of the large and broad cartilage-area ; 
scars in general brownish, oboval or suborbicular. Var. A (type). 
Folds few, scarcely imbricated. Var. B. Folds more numerous, im- 
bricated or even squamular where crossed by the rather distant 
lamelle. Var. C. Roseate-brown: folds numerous, subangulated, 
closely imbricated, obsolete above. 5 or 6. China? Var. C. from 
LL. Hood's Island. 
O. Turprnata. Lam. 44.—(? Ch. f. 668.) Oval, dark brown, 
depressed near the ventral edge, obliquely turbinated near the beaks, 
strongly plaited by large transversely wrinkled folds: inner edge 
blue, not scabrous. 33. Indian Ocean. “ Allied to O. Crista- 
GALLI” (Lam.), of which it may possibly prove a variety. 
O. Crista-GaLii.—(Arg. t. 20, f. D—Kn. 5. t. 16, f. 1.)\—Myrinus 
C., Lin. 1155.—D. p. 299.—W. t. 12, f. 1.—O. C., Ch. f. 683, 4.— 
Lam. 45.—E. t. 186, f. 3, 4, 5.—Sow. G.—Reeve, Syst. t. 121, f. 2. 
Obovate, tolerably strong, granular, not flaky, unarmed, of an uniform 
tint, ranging from ferruginous to livid purple, with large angular 
radiating folds, that vary im number, and extend almost to the 
incurved beaks: valves almost alike, the lower with a tendency to 
form elongated processes of attachment: mner margin scabrous in 
one or both valves. 3. Indian Ocean; frequently in grou, s, but not 
attached by the entire surface. 
O. Hyorts.—(Gualt. t. 103, f. A.)—Myrinus H., Lin. Sys. 1155 ; 
Mus. Ulr. 538.—D. p. 300.—W. t. 12, f. 2.—O. H., Ch. f. 685.— 
Lam, 47.—E. t. 186, f. 1— Desh. EF. 2, p. 298. Suborbicular, more 
