TRIBE OSTRACEA. 303 
white: lower valve attached by its entire surface, usually spreading 
at the sides near the hinge: edges simple, not wavy, very coarsely 
toothed internally towards the apex: inside of a rich purple-lake, or 
whitish, tinged with that colour in parts, and somewhat iridescent : 
scar subreniform: cartilage-cavity large. 6. Guacomayo, Cent. 
America. 
O. Lame ttosa. Phil (as of Broccut) 1, p. 88; 2, p.63. Elongated 
and beaked var. O. Cyrnusu, Payr. Cat. Cors. 79, t. 3, f. 1, 2.— 
Desh. ed. Lam. 7, p. 236. | Ovate or obovate, usually elongated, 
longitudinal, thick, but light (the structure not being compact): 
valves almost equal, moderately convex ; the upper one covered with 
large membranaceous lamellz, which are ochraceous or pale olive at 
their commencement, flattened (at times slightly undulated), choco- 
late-coloured, and free at their extremities: lower valve often very 
thick or else solid, rarely presenting sculpture or colouring, some- 
times stained with orange or with linear violet rays, still more rarely 
exhibiting numerous obsolete radiating costelle : beaks more or less 
prominent: inside greenish white, at times tinged here and there 
with pink or flesh-colour, denticulated near the hinge and edged with 
a yellowish olive border of the external flakes: scar moderate. 5. 
Mediterranean. In specimens from Lake Fusaro the lamine of 
growth are so loose that the shell almost appears in a state of dis- 
integration. 
O. Uncinata. Desh. Exp. Sc. Mor. 126, t.18, 9,10, 11. Very 
like Lame tuosa, but more solid, and, from the distinct and crowded 
radiating plications of the compact lower valve, having that margin- 
regularly closely yet not. angularly folded, which produces similar 
indentations in the flaky margin of the upper valve. 3. Greece, 
Smyrna. Possibly a variety of LAMELLosa. The upper valve is of a 
pale olive, mottled with chocolate-brown; the lower is dirty white. 
The shape varies infinitely; one of the individuals now before me 
exactly resembles Deshayes's figure, being longitudinally ovate and 
having tts beaks greatly incurved ; another is transversely trapeziform, 
and strongly reminds one of the types of TRAPEZINA in the Museum at 
Paris. 
O. Raricosta. Desh. E. 2, p. 299. Elongated, narrow, much 

' O. Srentina of Payraudeau (Payr. Cat. p. 81, t. 3, f. 3.—Desh. 
ed. Lam. 7, p. 236) appears from its figure to approximate closely to 
this species. I subjoi its description :—* Oblong, flattened, ashy- 
white; lamelle imbricated and undulated; upper valve flat or 
slightly convex ; margin strongly denticulated ; inside white. Medi- 
terranean.” 
