GENERAL DISCUSSION 



15 



TABLE III. DISTRIBUTION OF NORTHEAST ASIATIC LAND 



and fresh water shells. — Continued. 



Name of Species. 



Aplexa hypnorum 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 



Sphaerium corneum L 



Sphaerium lacustre Miiller 



Sphaerium asiaticum Mts 



Corneocyclas amnica Miiller 



Corneocyclas abdita Hald , 



Corneocyclas fontinalis Pfr 



Corneocyclas sequilateralis Pr , 



Corneocyclas sibirica Clessin , 



Cristaria herculea Midd 



Cristaria plicata Leach 



Anodonta beringiana Midd 



Anodonta woodiana Lea 



Margaritana margaritifera L 



Unio pictorum L. var. longirostris RSssmassler 



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- 



