NORTHWEST COAST MARINE SHELLBEARING MOLLUSKS. O 



The latest previous list for the region, that of Carpenter, enumer- 

 ates 468 species. Of the fauna as now enumerated, 13G forms are 

 common to the Atlantic waters, nearly all belonging to the Arctic 

 seas. There are a few species from the western part of Bering Sea 

 which might more properly be assigned to the Okhotsk or Asiatic 

 fauna, which is generally quite distinct from that of the American 

 shores, but I have thought it best to include them as they may extend 

 to the western Aleutians. The plateau fauna of the shallow part of 

 Bering Sea, which is also in the main distinct from that of the sur- 

 rounding coasts, has not been segregated from the Aleutian group 

 owing to the fact that thorough collections have not been made, and 

 in the present state of our knowledge it is impossible to be certain 

 how many and which species arc exclusively confined to the plateau 

 group, which consists largely of Buccinidae. 



The fauna of Kamchatka and the Okhotsk Sea, besides a large 

 number of endemic species, contains many analogues of forms 

 peculiar to the American coast, but specifically distinct from the 

 latter. This is probably due to the chasm of deep water extending 

 from the area between the end of the Aleutian chain and the Kussian 

 possessions. This abyss extends northward east of the Commander 

 Islands almost to Bering Strait, heading near the entrance to Plover 

 Bay on the Siberian side. The separation of the two areas has ap- 

 parently existed long enough for the modification of the American 

 and Okhotsk faunas to specific differences in many originally identi- 

 cal forms. 



We find also a certain number of species still persisting in the 

 region of North Japan, the Kuril Islands, and southern Kamchatka, 

 which are also found in the Oregonian and northern California 

 faunas, but not in the Aleutian region between their present habitats. 

 These are probably relics of the time when warmer seas extended to 

 the north and a gradual refrigeration exterminated them in the inter- 

 vening area. Such a species is II allot is kamchathana. 



The Tertiary and Pleistocene fossils of the shores of Bering Sea 

 also bear evidence of a communication with Atlantic waters during 

 the prevalence of more genial conditions. Several species now living 

 in Bering Sea are found fossil in the late Pliocene of Sankoty Head, 

 Nantucket, and the Pliocene of Iceland, and conversely the common 

 periwinkle of New England, Littorina palliata Say, is one of the 

 species found in the elevated beaches of the Nome district. Alaska, 

 and now extinct on the Pacific side. Evidently the intercommunica- 

 tion must have been tolerably free between the two oceans at the 

 time, though now there are quite pronounced differences between the 

 Greenlandic and the Berinjr Strait Arctic assemblies of mollusks. 



