Bulletin American Museum of Natural History. [Vol, XIX. 



of the young-of-the-year specimens are from two-thirds to 

 practically full grown, and differ scarcely at all from the post- 

 breeding pelage of the adults, except that perhaps the sides 

 and the ventral surface are a little paler. 



The contrast between these two series, taken only ten days 

 apart, at the same locality, is surprisingly marked, especially 

 when the most advanced adults and largest young-of-the-year 

 of the last set are contrasted with the breeding females and 

 half -grown young of the first set. 



The series taken at the head of the Shesley River,, two to 

 three weeks later, are quite similar to the more advanced of 

 the August 9 series from Summit, at the head of Telegraph 

 Creek. All of the Shesley River specimens, however, have 

 acquired the winter pelage, while many of the August 9 

 specimens are still in change, and some are still almost wholly 

 in the worn, faded, breeding pelage. 



Most of the 59 specimens in the present collection are 

 young-of-the-year; n of the females, however, give evidence 

 of having suckled young; and 7 of the males are obviously 

 adult. The 18 unquestionably adults measure as follows: 7 

 males, total length, 334 (318-349); tail vertebrae, 86 (75-92); 

 hind foot, 52 (47-56); ear, 11.4 (11-12): n females, total 

 length, 324 (308-339); tail vertebrae, 86 (78-100); hind foot, 

 50.4 (48-54); ear, 11.5 (9-13). 



In size and proportions this species closely resembles Citellus 

 columbianus, which it also more nearly resembles in general 

 coloration than it does most members of the parryi group. It 

 is, however, less strongly colored throughout, and has the 

 central area of the lower surface of the tail rufous instead of 

 gray; besides, it is much smaller and differs strikingly in 

 cranial characters. 



Mr. Osgood's S. empetra plesius is very closely related to, 

 if not identical with, what is here recognized as erythrogluteius 

 Richardson (Arctomys parryi var. B. erythrogluteia Richard- 

 son), the type locality of which is "the Rocky Mountains, 

 near the sources of the Elk River, in latitude 57." This is 

 very near the localities at which my present large series of 

 specimens was collected ; and there is reason to suppose that 



