132 
OSTREA. 
Shell somewhat orbicular, fiat, thin, semitransparent, 
quite smooth and glossy, except a few faint transverse 
wrinkles, white or pale grey, sometimes mottled with 
brown; the valves nearly equal: ears unequal, one of them 
very large, the other small, slightly striate longitudinally; 
inside glossy white : length half an inch; breadth not quite 
so much. 
From the plain variety of O. sinuosa it may at once be 
distinguished, by the want of the very fine decussate strise, 
with which that shell is always marked. 
At the time Captain Laskey recorded his O. similis, the 
true characters of O. laevis and O. ohsoleta were not clearly 
understood : and as the only distinction between his shell 
and the O. lcevis is the want of the striae towards the mar- 
gin, at that time supposed to form one of its essential 
marks, it can now only be considered as O. leevis. 
Western coasts, and North Britain: very rare. v. ft. 
9. Ostrea tumida. Tumid Scallop. 
Shell somewhat orbicular, flattish, glossy white, trans¬ 
parent, quite smooth: valves equal, with the sides un¬ 
equal, both of them rounded, but one of them produced: 
beaks pointed, not quite central; hinge straight, with the 
ears rather large, equal, and quite smooth ; inside white, 
smooth, with a large chalky patch in the centre, the mar¬ 
gin plain : length a quarter of an inch; breadth rather more. 
A single specimen only of this shell has as yet occurred 
to us, taken from the cavities of a large mass of the Ser- 
pula complexa, and which was dredged up at Torbay. It 
is entirely unlike any other species with which we are ac¬ 
quainted ; and in consequence of one of the aides being 
more tumid or produced, the breadth somewhat exceeds 
the length, v. v. 
1 0. Ostrea glabra. Mottled Scallop. 
Montagu, pi. 28. f. 6. 
SbeJi rounded, thin, nearly smooth but not glossy, mo${ 
minutely striate transversely, with seven rounded and 
slightly raised rays, mottled with rufous brown and yellow: 
ears large, nearly equal, one of them reticulated, the other 
only striate; inside marked y/ith twenty-one slender rays, 
the 
