MOLLUSKS 311 



Indies, the Gulf of Mexico, and the coast of Central America. 

 Strangely enough, the mollusks of the west coast of Florida are 

 more nearly related to those of the transatlantic province than 

 are the shells of the east Florida coast. This remarkable fact in 

 geographical distribution can only be explained by assuming that 

 an open waterway once existed across the northern part of the 

 Florida peninsula, connecting the Atlantic and the Gulf, through 

 which a mingling of the shallow-water forms from Georgia, the 

 Carolinas, West Florida, and the Gulf coast took place. Thus it 

 would appear that when Florida was an island the fauna of its 

 east coast, originally largely Antillean, was less disturbed by the 

 southern migration of American species. The Florida Keys are 

 essentially Antillean. The Caribbean or Autillean fauna is an 

 exceedingly rich and varied one. Among the most prominent 

 genera which may be encountered upon the Florida coast are 

 Strombiis, Fasciolaria, OUva, Marginella, Natica, Sigaretus, Littorina, 

 Tectarius, Neritina, Melongena, Cardium, Callista, Tellina, Lucina, 

 and Cyrena. ' In such an extensive and rich faunal province one 

 must not expect to find in any given locality a representation of 

 all the characteristic genera. For instance, collections made at 

 Havana, at Nassau, and at Vera Cruz would each contain forms 

 more or less peculiar and local, but certain species would be found 

 in each collection. 



On the west coast of America quite the same faunal division 

 into more or less well-marked provinces is to be found. Bering 

 Sea belongs to the arctic province, and contains, with Labrador 

 and Greenland, many identical forms. 



THE ALEUTIAN PROVINCE 



The shore waters from the southern peninsula of Alaska down 

 to about Vancouver comprise the Aleutian province. Within 

 this area occur some arctic species, notably the soft-shell clam, 

 Mya arenaria, which the fishermen gather in such large quan- 

 tities for bait along the Maine coast. An increasing number of 

 species common to this west-coast faunal region and to the 

 boreal province of the east coast are being recorded. Some of 



