Mammals 47 



Colorado, but is rarely found south of the Arkansas River. Mr. 

 Warren reports that it was taken at Monon, near the Kansas line. 



The Heteromyidae also have cheek-pouches, but are dis- 

 tinguished by the hind limbs, which are adapted for jumping. 

 As Miller and Gidley put it, the external form is murine or salt- 

 atorial. The typical genus (Heteromys) is found in tropical 

 America. We have in Colorado the genera Perognathus of Wied, 

 the pocket mice, and Dipodomys of Gray (also called Pero- 

 dipus) the kangaroo rats. Warren* cites six kinds of Pero- 

 gnathus from Colorado. These animals are readily known from 

 Dipodomys by the shorter tail, less than half the total length, 

 and the rooted tuberculate molar teeth. P. hispidus paradoxus 

 of Merriam, the Kansas pocket mouse, occurs on the eastern 

 plains. It is much the larger species, the total length over eight 

 inches. P. fasciatus infraluteus of Thomas, found at Loveland, 

 is readily known from all the others by the buffy under parts. 

 It is five inches long. P.flavus of Baird, widely distributed over 

 the plains, and extending up the Arkansas River to Salida, is the 

 smallest of all, length four and one-half inches or less. It is pale 

 buffy above, lined with black, the under parts white. Another 

 species of the plains region is P. flavescens of Merriam, larger than 

 P.flavus, but otherwise very similar. In southwestern Colorado 

 may be found the Apache pocket mouse, and according to War- 

 ren's latest opinion, the form is not typical Apache, but the 

 darker animal which Osgood named P. apache mclanotis, from 

 specimens obtained at Casas Grandes in Chihuahua. There is 

 however still another race, P. apache caryi of Goldman, dis- 

 covered eight miles west of Rifle. 



The beaver (Castor canadensis) has been dealt with so fully 

 in easily accessible works** that it is not necessary to describe 

 its structure and habits here. The Colorado beaver is not the 

 typical C. canadensis, but has been referred to the subspecies 

 frondator of Mearns, described from Sonora, Mexico. Although 

 beavers occur at various altitudes, they appear to range up and 



*The Small Mammals of Colorado. Colorado Mountain Club, 1921. 



**Enos Mills, In Beaver World (1913); A. Radclyffe Dugmore, The Romance of the Bea- 

 ver (no date, but later than 1913). See also E. R. Warren, Some Interesting Beaver Dams 

 in Colorado, Proc. Wash. Acad. Sci. VI (1905): W. P.Taylor, The Status of the Beavers of West- 

 ern North America, with a Consideration of the Factors in Their Speciation, U. of Calif. Publ. 

 Zoology, XII (1916); F. H. Holden. Osteological Relationships of Three Species of Beavers, 

 U. of Calif. Publ. Zoology, XVII (1917). 



