1916.] 



INTEODUCTION". 



9 



In the present paper two subgenera of Cynomys are recognized. 

 These are equivalent to the black-tailed and the white-tailed groups. 

 One new subspecies is described and one currently recognized name 

 is placed in synonymy, leaving the number of recognized forms at 

 seven, the same as in the last (1912) general list of North American 

 mammals.^ 



PELAGES AND MOLTS. 



In all prairie-dogs, except Cynomys mexicanus, there are two well- 

 marked annual molts over the entire animal, except on the tail, where 

 there is only a single renewal each year. The two coats are the harsh, 

 thin, summer pelage and the soft, heavily underfurred winter pelage. 

 In southern States, where the spring molt takes place much earlier 

 than in the North, the two renewals are conspicuous. Farther north 

 and at greater altitudes, where the season is shorter, the summer coat 

 is so little worn and the fall renewal so subtle that the autumnal 

 change is difficult to detect. 



In general, the spring molt begins on the pectoral region and axil- 

 laB, and the entire underparts from front to back are completely 

 renewed before any real molt is visible above. On the upperparts. 

 the head and shoulders, with occasional irregular areas on the back, 

 renew first, and the renewal progresses posteriorly. Considerable 

 wear is apparent over the anterior haK of the back before the tail is 

 in fresh coat. It is quite common to find museum specimens in full 

 summer coat except for the tail, which retains the old pelage of the 

 previous winter. In late summer or early autumn, at about the time 

 when the tail is at last in fuU fresh pelage, the winter coat begins to 

 appear on the extreme posterior parts of the body. The renewal of 

 the underfur progresses anteriorly in a regular definite area, and the 

 fresh, soft winter coat gradually covers the whole body. The 

 autumnal renewal thus exactly reverses the order of progression in 

 spring. The whole process is much as if there was a continuous 

 summer change of hair which started at the nose in spring, worked 

 backward to the tail, reversed, and in faU traveled forward to the 

 nose again. The tail, midway in the route of this process, receives 

 only one coat annually. 



There is, naturally, a considerable variation in the season of 

 renewal according to latitude or altitude. Breeding females are 

 always slow to acquire the fresh coat, renewal being greatly retarded 

 by lack of excess vitality. Young animals of the first year do not 

 molt or renew at the same dates as do adult males and nonbreeding 

 females which have hved over one winter. The molt of Cynomys 

 mexicanus appears to be much more complex than in the more north- 

 em forms and is almost continuous. Some individuals of this spe- 

 cies show parts of three distinct pelages. 



1 MHler, G. S., jr., Bull. 79, U. S. Nat. Mus., pp. 294-295, 1912. 



