THE COMMON MARINE SHELLS OF THE BOMBAY SHORE. 345 
DIVISION III. 
This comprises all the oysters, and I give the following extract from 
the paper already mentioned :— 
Ostrea crenulifera (Sow.)=plicata (Chem), 
Ostrea bicolor (Hanley). 
We give these names as most closely corresponding to the Bombay 
specimens that have come under our notice, but this genus is so widely 
distributed in all seas and the similarity of shell sculpture is so close, 
whilst the shape is so varied, that it is impossible to speak with abso- 
lute certainty. 
O, lacerata (Hanley).—Found on stones at low tide, densely clustered 
and arranged vertically. 
Of the genus Anomia we have two species. 
A. acheus (Gray).—A translucent, silky, copper-tinged (yellow to 
red) shell with often a roughly wrinkled exterior and a very polished 
metallic interior. The lower valve is flat and has a large circular or 
oval hole extending to the middle of the valve through which the 
byssus passes. The animal lives attached to rocks or stones, and, like 
the oysters, adapts itself in the shape of its shell to its surroundings. 
Muscular impressions central and so close together as often to make 
one scar. 
Hinge-teeth absent. 
Size about 14" 14". 
Placuna placenta (Linn.).—Circular, very flat and thin discs, often 
as large as a saucer. Texture like mica or talc, smooth towards the 
umbo, otherwise finely wrinkled with minute thread-like shining lines, 
Young shells faintly pink-tinged ; old ones often blackened with mud, 
otherwise they are white. In the interior at the umbo there are two 
diverging ridges. 
The Pectens.—These well known scallop (expanded fan-shaped) shells 
are only represented here by one or at most two species. Umboeg 
pointed and angular, and with wings or ears on either side; ventral 
border semi-circular, 
P. singaporinus (Sow.) has about 21 ribs, is whitish and generally 
densely covered with transverse bandings or blotchings of dark brown 
or rusty-red. 
