l6 LAND AND FRESH WATER MOLLUSKS 



tives of the fauna disappear among the islands of the Aleutian 

 chain. In British Columbia a few species belong to the valley 

 region between the Rockies and the Cascade Mountains, and 

 do not reach the sea coast, but these are too few to modify 

 perceptibly the general rule, and as a matter of fact they, like 

 the valleys themselves, soon disappear after crossing the 49th 

 parallel. 



Very much the same thing is true of the birds, as I was able 

 to demonstrate some thirty five years ago ; and even the marine 

 mollusks of the Alaskan coast form a somewhat analogous 

 assembly. 



The other two faunas concerned are those (i) of Asia, or 

 rather eastern Siberia, that part of Asia nearest to Alaska, and 

 (2) the Holarctic or circumboreal group of species which are 

 common to the entire boreal zone and characteristic of it, though 

 rather few in number. 



In referring to the Canadian fauna it will of course be clearly 

 understood that the fauna of that part of Canada discussed in 

 this paper and not the entire fauna of the whole Dominion is 

 meant. With this reservation we may proceed to discuss the 

 matter from the statistical point of view. 



One hundred and forty seven species or strongly marked 

 varieties are enumerated here from the Canadian region as 

 above limited, and fifteen other forms are mentioned which 

 though not known to cross the boundary yet in all proba- 

 bility will eventually be found to do so. By reference to 

 the preceding tables the extension of each species will be 

 found recorded, and the particular localities as far as discov- 

 erable are enumerated in the following text. Forty one spe- 

 cies are known from the Alaskan extension of this fauna 

 north of the Alaskan Mountains, or characteristic of that part 

 of the territory. Half of these are circumboreal or Holarctic 

 forms. 



The fauna of British Columbia, or the British Columbian 

 extension of what I many years ago designated the Oregon- 

 ian fauna, comprises seventy five species, so far as known, to 

 which in all probability should be added some thirty eight which 

 are known to approach the parallel of 49° from the south and 



