TRIBE OSTRACEA. 303 



white : lower valve attached by its entire surface, usually sp reading 

 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. Lamellosa. Phil (as of Brocchi) 1 , p. 88 ; 2, p. 63. Elongated 

 and beaked var. 0. Cyrnusii, Payr. Cat. Cors. 79, t. 3, /. 1, 2. — 

 Desh. ed. Lam. 7, p. 2-36. 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 lamellse, 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 costellse : 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 lamina of 

 growth are so loose that the shell almost appears in a state of dis- 

 integration. 



O. Uncinata. Desh. Exp. Sc. Mor. 126, 1. 18,/. 9, 10, 11. Very 

 like Lamellosa, 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 Deshayess figure, being longitudinally ovate and 

 having its beaks greatly incurved ; another is transversely trapeziform, 

 and strongly reminds one of the types of Trapezina in the Museum at 

 Paris. 1 



0. Raricosta. Desh. E. 2, p. 299. Elongated, narrow, much 



1 O. Stentina of Payraudeau (Payr. Cat. p. 81, t. 3, / 3. — Desh. 

 ed. Lam. 7, p. 236) appears from its figure to approximate closely to 

 this species. I subjoin its description : — " Oblong, flattened, ashy- 

 white ; lamellae imbricated and undulated ; upper valve flat or 

 slightly convex ; margin strongly denticulated ; inside white. Medi- 

 terranean." 



