United States National Museum - si-pddr - Smithsonian Institution

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 surrounding
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 apparently
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 intervening
area. Such a species is IIallot 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.