OSTREA OYSTER, SCALLOP. 177 



requires but little to satisfy it. The only nou- 

 rishment they need is brought to them by the 

 ever-flowing waves, and they scarcely exhibit 

 any symptom of life, but that of opening their 

 valves to receive the water, and then closing them 

 for security. Firmly attached to the rocks, and 

 enclosed within their strong testaceous dwelling, 

 they are protected against surrounding dangers. 

 Some of the species effect a change in their posi- 

 tion by a curious contrivance ; they manage to 

 bolster up one valve in the sand or mud, and 

 having thus fixed themselves erect, they open 

 their shells, and the flowing or reflux of the tide 

 forces them over by the pressure of the water 

 The animal has neither siphon nor foot. 



OSTREA Edulis. 



COMMON OYSTER. 



Specific character. Shell more or less orbi- 

 cular, inclining to oval, but subject to much vari- 

 ation in form and size, very irregular, imbricated 

 with scaly laminae ; upper valve small and flat- 

 tened, the other convex ; inside pearly white, 

 outside dull brown. 



Oysters are generally found with their lower 

 valves fixed to rocks or loose stones, and fre- 

 quently to one another. Most of our rocky 

 coasts abound with these shells, but Essex and 

 Suffolk chiefly are celebrated for them. They 

 are dredged up by a kind of net, with an iron 



