406 PROCEEDINGS OF THE ACADEMY OP [July, 



of data regarding the former abundance of the species in the region in 

 question. Where, however, a typical plains form, as Putorius nigripes 

 or Citellus tridecemlineatus pallidus, is found in the higher mountains, 

 I believe we are justified in concluding that they have migrated 

 outside of their proper habitat. 



Sciurus ludovicianus. 



This species is now quite common in the neighborhood of Greeley, 

 where I understand it has been introduced from Omaha. It is also 

 present in Denver. 



Citellus tridecemlineatus pallidus. 



The presence of this spermophile at Divide,^^ altitude 3,000 m., and 

 elsewhere in the mountains,^^ indicates a westward and upward move- 

 ment of this species from its center in the Great Plains, probably de- 

 pendent upon the presence of its physical habitat, the grass-sage- 

 brush plains in some parts of the mountains, rather than upon 

 temperature. 



Peromyscus nebracensis- 



This is another plains form of Upper Sonoran and Transition zones 

 which appears to be invading the mountains, judging by its occurrence 

 at an altitude of 3,508 m.^^ and elsewhere through the mountains. 



Phenacomys preblei. 



The only record hitherto of this species is that given by Merriam^^ 

 from Long's Peak. I have taken a single specimen on North Boulder 

 Creek at about 2,900 m. altitude. This is the only specimen I have 

 secured in spite of careful trapping in several places. 



Spilogale tenuis. 



I have taken a few of this species at Boulder, hitherto known only 

 from Arkins and Estes Park. 



Putorius nigripes- 



The occurrence of the black-footed ferret at an altitude of 3,124 m.^* 

 indicates a probable migration on its part from its habitat on the plains 

 into the mountains. 



" Fide Warren (op. cit., p. 242). 



'^ Bailey, V: The Prairie Ground Squirrels of the Mississippi Valley, Bull. 4,. 

 U. S. Biol. Survey, gives its western limits as approximately Twin Lakes. 



" Fide Warren (op. cit., p. 245). 



" Merriam, C. H. : Phenacomys preblei, a New Vole from the Mountains of 

 Colorado, Proc. Biol. Soc. Wash., Vol. XI, p. 45. 



" Fide Warren (op. cit., p. 264). 



