THE OYSTER. 
45 
.olivaceous, and sometimes stained with purple. 
The Eastern Oyster, Ostrea virginiana , is the 
common exotic species. They are brought here 
by the car load, when young, and planted in the 
shallow waters of San Francisco Bay. They 
mature in from one to three years, and though 
they thrive in our bays ; very few of their ova 
develop, probably on account of the coldness of 
the water. 
Somewhat resembling the oyster, is the cu- 
rious genus of which we have one representa- 
tive, Anomia lampe , Gray. The shells are thin 
and translucent, silvery or golden. The lower 
valve is Hat and pierced by a hole ; the upper 
valve is arched and marked by several muscular 
impressions. This species is generally found in 
southern waters and on the coast of Mexico, but 
I found one living specimen at Monterey. The 
shells are somewhat circular in form, about an 
inch and a half in diameter. A more northern 
species belonging to this family is Placuanomia 
macroschism,a , Desh., Fig. 1, PI. XII, gives an 
internal view of the upper valve of one speci- 
men, showing the curious star-shaped muscular 
impression, with a smaller one below it. The 
form of the shell varies very greatly, though its 
normal shape is circular. The under valve is 
pierced, and both of them are strong, pearly 
within, and of a greenish white color. It some- 
times grows to the size of a large oyster. It can 
always be recognized by the muscular impress- 
ion, which looks like the imprint of a seal. 
Of the pretty Comb-shells or Scallops, there 
is a good deal of variety in form and color. We 
