. 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 flat 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 

 macroschisma, 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 



