246 THE MOLLUSK FAUNA OF NORTHWEST AMERICA. 



was begun when the Steamer Albatross, of the U. S. Fish Commission, came 

 "round the Horn" and began to explore the deeper waters of the coast. Her 

 dredgings have extended from Patagonia to Bering Sea, and from Panama to 

 the waters of Japan and the Okhotsk Sea. The collections of mollusks were 

 merely incidental to her other work but aggregate a very large total, and com- 

 prise much very precious material. The collections of the Revenue Marine in 

 the Bering and Polar Seas south and north of Bering Strait deserve mention, and 

 also those made by members of the U. S. Geological Survey, both of recent and 

 Pleistocene or even older material. 



The present writer during eleven years spent on the coast of Alaska in the 

 U. S. Coast Survey hydrographic work, made a very large collection, now in the 

 National Museum, which also acquired the collection of the late Dr. R. E. C. 

 Stearns. 



This material, supplemented by the generous aid and donations of many 

 private collectors, has resulted in bringing together a collection not only more 

 extensive than that in any other museum, but it may also be said more extensive 

 than that of all other museums put together, for this particular fauna. It is 

 hoped within a reasonable time to make it the basis for a general manual of 

 northwest coast shells, though there is no doubt that the improved methods of 

 collecting, the increased number of collectors and the more thorough exploration 

 of all parts of this immense stretch of coast, will furnish a supply of novelties for 

 many years to come. 



While the study of these collections is far from complete, yet a great deal 

 of work has been done upon them and it is possible to formulate some tentative 

 general conclusions in regard to the Pacific coast faunal relations, as indicated by 

 both the recent and fossil material. 



One of the most interesting facts brought out by the Albatross dredgings 

 in the Okhotsk and Japan seas is that the two faunas, the American and Asiatic, 

 are almost perfectly distinct. Excluding the polar fauna of the Arctic seas, 

 which is limited in species and circumboreal in distribution, and which sends 

 a few members southward on both coasts, the number of species common to the 

 opposite shores of the Pacific is astonishingly small. Even the narrow channel 

 of Bering Strait divides many of the species, a fact which may be connected 

 with the southward current of cold water which washes the Asiatic coast from 

 Bering Strait to the Kurile Islands, while on the American side the drift is of 

 water warmed over the shallows of that part of the sea and in Norton and Kotze- 

 bue sounds, and moved northward along the coast by the tides and a combination 

 of other physical factors. 



The vast submarine plateau, which occupies the northeastern portion of 

 Bering Sea and is covered by only 100 feet of water or less, has a special fauna 

 of its own, differing from the shore fauna nearest to it and having many peculiar 

 species. The gap between it and the shore fauna may perhaps be connected 

 with the action of ice in winter near the shores, which does not operate in water 



