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, Chrysodomus, 
Sipho, Trophon, Bela, Velutina, Trichotropis, Lacuna, Margarita, 
Pecten, Leda, Yoldia, Astarte, and Mya. 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 (Lunatia 
and Neverita), Acmea, Margarita, Chiton, Doris, Afolis, Mytilus, 
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 
