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THE AMERICAN NATURALIST [Vol. XLVIII 



the total of mammalian forms, but the totals for each 

 order and for each family. 



In comparing the three areas in which all the life zones 

 are involved, the truth of the effect of extended distribu- 

 tion on speciation is still more forcibly impressed upon 

 us. In this case we are comparing areas which are suc- 

 cessively larger in size, the San Jacintos, with their foot- 

 hills and low passes involving the fauna of an area of 

 about 2,500 square miles, the Sierras, about 60,000 square 

 miles, and the whole state of California about 158,000 

 square miles. The following table, derived from Table 

 III, is very significant in showing the diminishing in- 



Ungulates I 2 3 4 2 7 10 1.00 2.33 2.50 



Rodents 16 28 31 41 110 203 2.56 3.93 6.45 



Carnivores.... 9 15 17 10 29 51 1.11 1.93 3.00 



Insectivores...! 3 5 6 3 12 20 1.00 2.40 3.33 



Cheiroptera ... 1 4_ 7 11 7 12 26 1 J5 1.71 2.36 



Totals 34 58 G8 63 I 170 310 1.85 2.93 4^ 



crease of genera, and the constantly increasing addition 

 of species as the area is enlarged. 



By comparing the upper zones of the San Jacintos 

 with the San Jacintos as a whole, and the upper zones of 

 the Sierras with the Sierras as a whole (see Table III), 

 we find that increasing the life zones has in a lesser 

 degree the same effect as increasing the geographic area 

 regardless of zones; in other words, adding life zones 

 tends to have the same effect on speciation as adding 

 faunas and associations without life zones. The follow- 

 ing table (derived from Table III) illustrates this : 



Another rough test of the hypothesis was made in a 

 comparison of the mammalian faunas of some of our 



