TRIBE OSTBACEA. 297 



arched at the other. Upper valve the smaller, flattish ; its lamellae 

 close-set, yellowish chocolate - coloured. Lower valve moderately 

 hollowed, dirty purple ; its distant lamellae arranged in rather nu- 

 merous radiating ribs. Inside wholly white, except at the margin, 

 which partakes of the external colouring. Denticles on one or both 

 sides of the cartilage : inner edge elsewhere simple. 2. Adriatic; 

 Black Sea. 



O. Cochlear. Poli, 2, t. 28,/. 28.— Lam. 5.— Phil, 1, p. 89. 

 From oval to suborbicular, very thin, scarcely, if at all, lamellated, 

 more or less tinged with rose-colour, glabrous ; upper valve concave 

 externally ; lower valve deeper and larger, sometimes with more or 

 less obsolete radiating ribs : inside whitish, its disk often stained 

 with rufous-purple, edges simple, a few cardinal denticles near the 

 apex ; scars placed nearer to the apex than to the rounded base. 2£. 

 Mediterranean. 



O. Cristata. Bom, t. 7, /. 3.—Poli, t. 28, /. 26, 7.— Phil. 1, 

 p. 88 ; 2, p. 63. — 0. C. var. C. Lam. 6. Ovate or orbicular, thin, ex- 

 panded : upper valve much the smaller, shallow, white, beneath the 

 concentric rows of dirty yellow imbricated flattened membranaceous 

 lamellae ; lower valve rather profound, usually attached at the apex 

 alone, whitish tinged with orange or pink, sometimes rayed with 

 crimson lines, its lamellae strong, distant, curly, and moderately 

 elevated, its folds arranged in radiating rows : inside silvery white, 

 having distinct denticles near the incurved and pointed beaks ; scar 

 moderate and reniform ; cartilage conical. — Var. 0. Depressa, Phil. 

 1, p. 89, t. 6,/. 3. Attached by the entire surface ; concentric flakes 

 few and distant ; a few rosy rays. 3. Mediterranean. The specimens 

 of Lamarck's Cristata in the Museum at Paris appear distinct, and 

 of ?nore than one species. The 0. Exalbida of Gmelin is founded on 

 Knorr, 5, t. 14,/. 4, which is apparently designed for a young example 

 of this shell. 



O. Gallina. Lam. 7. — Del, t. 18,/. 1. Obliquely ovate, small, 

 rounded on one side, subreniform, w r hitish, glabrous : upper valve 

 decidedly smaller, slightly convex : lamellae quite obsolete. — Var. 

 Lower valve rayed with violet-coloured narrow ribs. Atlantic ? The 

 figure of Delessert much resembles (except in colouring) one of the many 

 varieties of O. Rhizophor^e. It represents the interior as pure white, 

 and exhibits no indications of ribs or lamella on either valve. 1 



O. Lingua. Lam. 9. Thin, somewhat foliaceous, ovate-oblong, 



1 0. Numisma, Lam. 8, having been founded on a single wretched 

 specimen in the Museum which is destitute of any decided charac- 

 teristics, should be expunged from our catalogues. 



x 



