MAMMALS PECULIAR TO ALASKA 
93 
north-eastern Asia. Professor Engler* cites a large number 
of arctic-alpine plants, most of which are met with in these 
two regions, and extend southward in America along the 
Rocky Mountain chain. He argues that some of the species 
were probably capable of spreading from the one continent 
to the other under the existing conditions of land and water. 
Of others he does not consider that they could have drifted 
across the ocean by occasional means of transport, and he 
urges that only a former land connection in the north could 
satisfactorily explain their presence in Asia and North 
America. 
Finally a few observations on the land bridge problem from 
the marine faunal aspect may elucidate some doubtful points. 
Dr. Dallf divides the existing marine fauna of the north¬ 
eastern Pacific into three zones, viz., the Oregonian, Aleutian 
and Arctic. The Oregonian extends from Monterey to the 
Shumagin Islands. The Aleutian passes westward from the 
Shumagin Islands, includes the Aleutian chain, and reaches 
northward to the floating ice in Bering Sea, hounded by a 
depth of five hundred fathoms. The arctic zone stretches 
indefinitely southward beyond the five-hundred-fathom line, 
and is bounded in the north by floating ice, or water of thirty- 
two degrees. Some arctic species have crept southward to the 
northern islands of Japan and Cape Newenham, while a series 
of isolated arctic colonies occur from Cook’s Inlet southward 
and eastward. 
Dr. Dali’s views are mostly derived from a study of the 
marine mollusca, and it is interesting to note that in the 
main points they are confirmed by Miss Rathbun £ after an 
examination of the northern Pacific Crustacea. She states 
that arctic species often continue southward through Bering 
Strait, along the west coast of Bering Sea, to Okhotsk Sea and 
the Kurile Islands. Some of them extend eastward to Puget 
Sound and even further south. Miss Rathbun noticed that in 
exceptional cases, for instance Philyra pisum and Cancer 
* Engler, A., “ Entwicklungsgeschichte der nordl. Florengebiete,” 
pp. 22 — 43. 
t Dali, W. H., “ Marine Faunal Region of North Pacific,” p. 206. 
f Rathbun, Mary J., “ Decapod Crustaceans of North-West Coast,” 1 
p. 6. 
