482 WHEELER. 



hand, in the Huachuca Mountains of Arizona such neotropical forms 

 as species of Eciton, Odontomachiis, Pheidole, etc. are abundant at alti- 

 tudes of 4000 to 6000 ft.2 



Before considering the historical problems suggested by the ant- 

 faunas of the four regions of the tables, it will be advisable to analyze 

 them more closely. The total number of forms recorded for all the 

 regions is 422 distributed as follows : 



A B C D 



58 or 13.7% 60 or 14.2% 180 or 42.6% 124 or 29.4% 



In reality the total number of different forms is only 311. If we count 

 only the forms peculiar, endemic, or precinctive to each region (printed 

 in italics in the tables) we have the following: 



29 18 112 75 234 



There are therefore 77 forms common to two or more of the regions. 

 This would yield the following percentages for the given groups: 



A B C D Common 



9.3% 5.8% 36.0% 24.1% 24.8% 



The totdl number of endemic forms in the western fauna (A + B + C) 

 is 159 or 68%, whereas the 75 eastern forms represent only 32%. 

 The number of forms in common gives a good index of the affinities 

 of the different regions, and may be tabulated as follows: 



2 In his interesting paper on the insects of Custer County, Colorado, CockereU 

 (1893) does not accept Merriam's terminology for the life-zones of that region. 

 He distinguishes three zones, a "subalpine," up to about 6500 ft., a "mid- 

 alpine" between 6500 and 10,000 ft. and a "high-alpine" zone above the latter 

 elevation, and correlates these with Merriam's zones in the statement that "an 

 analysis of the insects of the Colorado Mountains shows that the high-alpine 

 and mid-alpine elements, though sufficiently distinct, are both essentially boreal. 

 If we foUow Dr. Merriam's arrangement, it appears that the high-alpine is 

 truly boreal, while the mid-alpine belongs to the transition region, containing 

 a considerable number of strictly American tj'pes. The subalpine, on the other 

 hand is southern or Sonoran." 



