MOLLUSKS 309 



shallow- water forms have been taken at great depths, but in 

 general the abyssal fauna is a peculiar one that cannot well be 

 marked off into geographical provinces. 



THE ARCTIC PROVINCE 



The east coast of America is divided into several molluscan 

 faunal regions. A series of very-cold-water forms belonging to 

 a circumpolar region, called the " arctic province," are found as 

 far south as Newfoundland. On the New England coast a num- 

 ber of these arctic species are also found, urged south by the 

 influence of the cold Labrador current. The most characteristic 

 genera belonging to this arctic fauna which are found upon the 

 Maine and Massachusetts coasts are Buccinum, Chrysodormis, 

 Sipho, TropJion, Bela, Velutina, Trichotropis, Lacuna, Margarita, 

 Pecten, Leda, Yoldia, Astarte, and My a. Examples of all these 

 genera are encountered as far south as Cape Cod. 



THE BOREAL PROVINCE 



A " boreal province " corresponds with a similar faunal region 

 upon the European shore. The mollusks which compose this 

 fauna are about three hundred in number, and range along the 

 New England coast from the Gulf of St. Lawrence to Cape Cod. 

 It is a somewhat remarkable fact that many of these species are 

 identical with English and French forms. The striking genera 

 upon the American side are Purpura, Littorina, Polynices (Lnnatia 

 and Neverita), Acnma, Margarita, Chiton, Doris, ^Eolis, Nytilus, 

 Modiola, Thracia, and Nucula. 



THE TRANSATLANTIC PROVINCE 



Cape Cod has been regarded, until very recently, as a sharp 

 divisional point between the boreal and the transatlantic prov- 

 inces, the latter faunal area extending down the Atlantic coast of 

 the United States to southern Florida. At Cape Cod the Labrador 

 current is deflected from the coast, and the warmer shore waters 

 south of that point are unfitted for the development of the boreal 

 forms, though some of them, as we shall see, have passed the 



