GENERAL DISCUSSION 



IS 



TABLE III. DISTRIBUTION OF NORTHEAST ASIATIC LAND 



AND FRESH WATER SHELLS. — Continued. 



Name of Species. 



Aplexa h)^norum L 



Carychium minimum Miiller 



Siphonaria thersites Cpr ... 



Valvata cristata Miiller 



Valvata piscinalis Miiller 



Valvata sibirica Midd 



Valvata stelleri Dybowski 



Vivipara limnseoides Schr 



Vivipara prserosa Gerstf. 



Vivipara ussuriensis Gerstf. 



Bythinia troscheli Paasch 



Bythinia kickxii Westend 



Bythinia striatula Benson 



Melania cancellata Benson 



Sphserium corneum L 



Sphserium lacustre Miiller 



Sphaerium asiaticum Mts 



Comeocyclas jimnica Miiller 



Corneocyclas abdita Hald 



Comeocyclas fontinalis Pfr 



Comeocyclas aequilateralis Pr 



Comeocyclas sibirica Clessin 



Cristaria herculea Midd , 



Cristaria plicata Leach , 



Anodonta beringiana Midd , 



Anodonta woodiana Lea , 



Margaritana margaritifera L 



Unio pictonim L. var. longirostris Rossm&ssler 



IV. CONCLUSIONS IN REGARD TO THE ALASKAN FAUNA. 



The fauna of Alaska, so far as the land and fresh water shells 

 considered in this paper enable us to judge, is composite. The 

 mollusks are characteristic especially of two, and to a much 

 smaller extent of two other, faunas. The former are limited 

 by topographic features. Thus the fauna of boreal Canada, in 

 constantly diminishing number of species, is extended to the 

 northwest, north of the Alaskan Range to Bering Sea on the 

 west and the Arctic Coast on the north. 



In like manner the fauna of the northern part of the Pacific 

 States is extended west of the ranges which in the north repre- 

 sent the Rocky Mountains, and between them and the sea, 

 northward into British Columbia and thence westward into 

 Alaska, south of the Alaskan Range, until the last representa- 



