TRIBE OSTRACEA. 807 
O. Doriwetia. Lam. 35.—E. t. 188, f. 4,5. Oblong, parasitical, 
whitish, with about 4 good-sized plaits on each side: back flattened 
and glabrous. 134. Sumatra. 
O. Frons.—(Arg. t. 19, f. D.—Myrivus F., Lin. Syst. p. 1155.— 
Born, 123, vignette at p. 121, f.b.—D. p. 301.—W. t. 12, f. 3.—O. F., 
Ch. f. 686.—Hanl. Conch. Mis. O. f. 5.—O. Rupetua, Limacetia 
and Eruceiya, Lam. 36, 37, 38.—O. Fortum, Reeve, Sys. t. 121, f. 3. 
—O. R., Cuvier, R. An. edit. Audouin, t. 72, f. 2. Very variable in 
shape, being sometimes oboval, sometimes elongated oblong or sub- 
fusiform, more or less solid, ranging in colour from purplish red to 
orange-yellow, adorned with radiating rib-like folds, that usually 
diverge, in the upper valve, from a more or less central dorsal rib, 
and in the lower valve from a corresponding hollow (caused by the 
GorGontA, a stalk to which the shell has adhered by its hook-like 
processes of attachment): folds not imbricated or armed, usually 
numerous, sometimes subangulated, sometimes obtuse, and generally 
stronger in the lower valve. Inside of a paler or richer yellow; 
inner margin of the upper valve rough with elevated granules: scar 
moderate, lateral, more or less reniform. 2. W. Indies. The 
O. Equrstris of Say (Am. Con. t. 58) may prove the young of this 
species. 
O. Fouium. Lin. Mus. Ulr. p. 5384.—Ch. f. 665, 6.—E. t. 184, 
f.13, 4.—D. p. 274.—W. t. 11, f. 62.—( Knorr, 1, t. 23, f. 2.— Rump. 
t. 47, f. A.— Klein (copied) t. 8, f. 22.) Oval, rather thin, purplish 
brown, attached to a stick, which causes the upper valve to present a 
more or less central elevated space corresponding with the cavity in 
the lower valve; sides obtusely and obliquely plaited; surface not 
lamellated: the edge not plicated, but simple: inside whitish or 
displaying the external coating, subnacreous: margins not scabrous, 
usually with a few granules near the cartilage. 24. Indian Seas ? 
I think that this species has been confused with many others, and 
consequently have restricted the name to the shell described in the 
Museum of Queen Ulrica. 
O. Lapretna. Lam. 40. Small, whitish, obliquely ovate, thin, 
pellucid, broader at the base; with a single row of oblique plaits ; 
upper valve with prickly scales. 3. China and Japan. The type 
in the French Museum reminds me of a young Fouium armed with 
incipient spiny tubercles, as in Hyoris. 
O. Purcata. Ch. 8, p. 34, f. 674, and Var. f. 680.—D. p. 275.— 
Lam. 41 (in part).—E. t. 184, f. 9 —W. t. 11, f. 63.—(Gualt. t. 104, 
f. A.) Very variable in shape, more or less longitudinally obovate, 
peculiarly light and lamellar in structure, upper valve generally the 
more convex, usually ashy with a purple tinge, purplish or rich 
rufous (often radiated with lines of a deeper colour), with numerous 
