MOLLUSCS. 



205 



marine, species being found in all but the colder seas. 

 In these forms the animals lie upon one side, and there 

 results an inequality of the valves. On our east coasts 

 oysters extend from the Gulf of Mexico to Cape Cod. 

 Further north (except in the Gulf of St. Lawrence) they 

 are not found native, but are 'planted.' The centre of 

 the oyster industry is Baltimore. In 1894 the oyster- 

 fishery of the United States amounted to over $16,000,000. 

 In the scallops (fig. 43) the shell is fluted, and the 



FIG. 43. Scallop (Pecten irrad.ia.ns}. From Binney's Gould. 



valves may be unequal or similar in shape. These mol- 

 luscs can swim freely by rapidly opening and closing the 

 valves of the shell; and thev are further noticeable from 



m/ 



the fact that around the edge of the mantle are a series of 

 rather complicated eyes. The ' scallops' of the markets 

 are the adductor muscles of these molluscs. In the pearl- 

 oysters the inner layer of the shell has a pearly appear- 

 ance, and these forms also produce, like some other mol- 



