302 TESTACEOUS MOLLUSCA. 
the umbones only, rayed with about 6 or 7 angulated ribs, pale rufous. 
Edges slightly wavy, but not plicated, neither scabrous nor denticu- 
lated internally. Inside whitish, often mottled with dirty purple. 
5. Tagus, Portugal. 
O. Ecutnata. Quoy and Gaym. Astr. 3, p. 455, t. 76, f. 13, 4.— 
O. Sprnosa, Desh. ed. Lam. 7, p. 237. Obovate or suborbicular, 
small, inequivalve, tolerably strong: upper valve shallow but convex, 
purplish black, with usually two whitish radiating streaks, armed 
with numerous irregularly disposed and moderately large perpen- 
dicular tubular spines: lower valve more capacious: inside dirty 
white, with usually a dark brown disk in the upper valve: hinge 
with adjacent cardinal denticles: beaks not projecting. Var. No 
distinet rays; the spines purplish black on a paler ground. Philip- 
pines and Amboyna. The only examples known to me are attached 
by the entire surface, but the lower valve is stated to be reddish, and 
adorned with a few spines. 
O. Sretiata. Gmel. 3837.—Schrot. Hin. 3, p. 877, t. 9, f. 7.— 
Copied as O. Cristarra, W. t. 11, f. 65. Very inequivalve, rather 
thin, sometimes suborbicular, sometimes elongated-ovate, almost 
always attached by the umbones, of lighter or darker shades of 
purple. Upper valve the smaller, nearly flat, or even concave ex- 
ternally, somewhat lamellar, the flakes depressed, in the younger 
specimens armed with more or less numerous tubular or semitubular 
spines that converge to the centre of the valve: lower valve profound, 
its lamelle distant and raised into projecting scales where they tra- 
verse the few obtuse and radiating ribs, which gives the margin (in 
perfect specimens) a beautifully foliated appearance: beaks acute. 
Inside whitish, usually stained in the middle of the upper valve 
with brown; a few rather indistinct cardinal denticles: cartilage 
conical, 1. Guinea (fide Schroter ). 
O. Prismatica. Gray, Ann. Phil. 1825.—? O. Inipxscens, Gray, 
Con. Mis. Os. f.6, 7. Longitudinally ovate or obovate, very solid ; 
valves rather, and nearly equally, shallow; upper valve, when fresh, 
covered with extremely close-set imbricated uncurled flakes of an 
ash-brown colour, under which the surface is smooth subnacreous 

' Mr. Cuming has taken, in the Philippines, some specimens, 
which may possibly prove aberrant forms of this species. They are 
of an orbicular shape, with thinly spread absolutely flat purplish 
flakes, adorned by two ill-defined yellowish white rays. The young 
are sprinkled with a few tubular spines (visible upon the umbones of 
the more adult examples), but these are entirely obsolete in aged 
individuals, which closely resemble CALLIcHROA. 
