152 University of California Publications in Zoolix/i/ [Vol. 10 



i 



In the second place, there are practically no exceptions to 

 the rule that the Boreal zones on the Sierras possess species and 

 usually genera distinct from those of the Sonoran zones of the 

 desert. We may cite here the coyotes, foxes, rabbits, wood-rats. 

 and spermophiles. If isotherms are so potent as harriers in 

 the case of other organisms it seems reasonable to expect the 

 sheep to have been limited in their distribution by these sunk 

 factors. It is thus, on distributional grounds, improbable that 

 sheep wander indiscriminately back and forth between the high, 

 cold Sierras and the hoi desert ranges, general assumption to 

 the contrary notwithstanding. 



Mr. Carr was especially instructed to gather all obtainable 

 information as regards this very point. Without here going 

 into detail, the gist of the information gathered by him from 

 mountaineers and residents of Owens Valley is that the Sierra 

 Nevada bighorns in the Mount Baxter region at the present time 

 do no1 range north of Taboose Pass, nor east across Owens 

 Valley, though they do descend the east slope of the Sierras to 

 I he foothills in midwinter. 



It is probable, therefore, that the Sonoran ami Boreal forms 

 of sheep do not intermingle, although their ranges in the Inyo 

 region closely adjoin. 



The treatment of the forms under discussion as subspecies 

 of one species, and the consequent adoption of the trinomial 

 form of name for each of them, is in accord with the now 

 dominant view of mammalogists. The most recent expression 

 I Allen. 1912, pp. 20, 21), is that there are two groups of sheep 

 in North America, the northern Ovis dalli group, and the south- 

 ern Ovis c< rvina group. These two groups are treated as distinct 

 species. It is to the second that the two forms inhabiting Cali- 

 fornia belong. It is not, however, to be inferred that anyone 

 has proven actual intergradation between cervina and sierrae, 

 sierrai and nelsoni, or nelsoni and a rvina. Whatever may have 

 been the geographic relations between these forms a century ago 

 is probably now beyond the possibility of proof. The forms 

 persist merely as isolated colonies of very much restricted range. 



