No. 567] EFFECT OF DISTRIBUTION ON SPECIATIOX 135 



To test the law by comparison of faunas of areas of 

 different extent, a series of tabular comparisons of the 

 faunas of various regions of different size and character 

 was made. In all of these tabulations, care has been taken 

 in the choice of areas for comparison to make them of un- 

 equal size from a distributional point of view, and to 

 make them reasonably comparable. An arctic and a 

 tropical region, for example, are not considered reason- 

 ably comparable as regards number of genera and 

 species, nor is a region on the outskirts of the range of a 

 group considered comparable with a region near its 

 center of distribution. 



Table III shows a comparison of the mammals of vari- 

 ous parts of California. The regions compared are as 

 follows: (A) the boreal and transition zones of (a) the 

 San Jacinto Mountain range, (b) the San Bernardino 

 Mountain range, and (c) the entire Sierra range, includ- 

 ing the Warner and Shasta Mountains to the north, and 

 the San Bernardinos and San Jacintos to the south; (B) 

 a comparison of all the zones of (a) the San Jacinto 

 Mountains with the immediately adjoining country, (b) 

 the Sierra range as denned above, and including their 

 foothills, and (c) the entire state. 



A careful study of Table III brings out a number of 

 interesting and significant facts, and bears out the law 

 here proposed with unexpected accuracy, barring one 

 seeming exception which, as we shall see later, can not 

 truly be considered as such. 



Let us compare first the three areas in which only the 

 two uppermost life zones are involved, and from which 

 the species invading only the lower Transition zone have 

 also been excluded. First, a word as to the areas com- 

 pared. The Boreal and Transition zones of the Sierras 

 take in over one half of all the representation of these 

 zones within the whole state. These zones of the San 

 Bernardino and San Jacinto mountain masses are, as 

 compared with the entire range, very small indeed, and 

 comprise almost as small areas as could justifiably be 



