TRIBE OSTRACEA. 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 lamelle rarely, if ever, raised; sur- 
face otherwise glabrous. Inside whitish, except near the edge, which 
is never scabrous: scar large, suborbicular. 6. Indian Seas.} 
O. Raprata. 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. 94...82. Indian Ocean. I am unable to identify this 
oyster, which “ Lamarck has probably founded upon an aged Hyortis” 
(Desh.). 
O. Mrcopon. Hanl. Z. P.1845.—O. Gatuus, 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 lamelle 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 affied by the apex 
solely, the plaits are smaller and quite marginal, leaving the central 
portion of the shell nearly smooth. 
O. Prs-rieris. Hanl. 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 Hyoris 
the 
O. Impricata. Lam. 46.—E. t. 186, f. 2, copied from Fav. t. 45, 
f. C.—Desh. E. 2, p. 298. Rounded, with very numerous angular 
folds, which are large at their termination, imbricated with lamelle, 
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. 
