TRIBE 0STRACEA. 309 



or less strong, of various shades of brown, with numerous angular 

 radiating folds, which are armed in both valves with subtubular 

 patulous spines ; the concentric lamellae rarely, if ever, raised ; sur- 

 face otherwise glabrous. Inside whitish, except near the edge, which 

 is never scabrous : scar large, suborbicular. 6. Indian Seas. 1 



O. Radiata. Lam. 48. — (Fav. t. 45, H.) Very large, convex, 

 rounded ovate, heavy, with regular crowded longitudinal imbricated 

 ribs ; margin serrated by folds : whitish within, except at the 

 margin. 9-f- ... 8f. Indian Ocean. I am unable to identify this 

 o)/ster, which "Lamarck has probably founded upon an aged Hyotis" 

 (Desh.). 



O. Megodon. Hani. Z. P. 1845. — 0. Gallus, Valenc. Venus, 

 t. 21. Solid, subequivalve, either of an uniform dusky purple or 

 mottled with purple on a greenish ground, elongated, incurved 

 posteriorly, so that the shell appears lunate, armed towards the 

 margin with about 5 or 6 enormous subangular tooth-like plaits, 

 which extend around the anterior surface only ; there being, likewise, 

 a few most indistinct angular little folds on the posterior side ; 

 glabrous, except upon the outer edge of the folds, where the succes- 

 sive stages of lamellae are distinctly visible. Inside white stained 

 with green, scar rather large and reniform, edges more or less 

 scabrous with small granules : beaks incurved. 5. Peru. When 

 attached by its entire surface, for it is usually affixed by the apex 

 solely, the plaits are smaller and quite marginal, leaving the central 

 portion of the shell nearly smooth. 



O. Pes-tigris. Hani. Z. P. 1845. Of an uniform tint, ranging 

 from deep purple to purplish red, solid, more or less oval, and often 

 subtriangular, in the more characteristic examples, from the abrupt- 

 ness of the produced and straightish posterior outline : the margin 



1 Deshayes, apparently with reason, regards as a form of Hyotis 

 the 



O. Imbricata. Lam. 46. — E. t. 186,/. 2, copied from Fav. t. 45, 

 /. C. — Desh. E. 2, p>- 298. Rounded, with very numerous angular 

 folds, which are large at their termination, imbricated with lamellae, 

 and armed with tubular scales : inner edges glabrous. Java. 



A small oyster, constantly met with in the boxes of Chinese shells, 

 is usually ascribed to the same species, as either the young or a 

 dwarf form of it. The colour is of a paler or darker reddish purple 

 (in very immature examples mottled with that tint on a whitish 

 ground) ; the folds are not decidedly angular, the structure is light, 

 and the spines or tubular scales for the most part depressed, and 

 sometimes undeveloped. 



