106 Proceedings of the Biological Society of Washington. 



Skull. — Similar to that of castanurus, possibly averaging a little larger; 

 decidedly smaller than that of cinerascens or of lateralis. 



Measurements. — Average of 6 adults from Wind River and Gros Ventre 

 ranges: Total length, 274.5; tail vertebrae, 95; hind foot, 40.7. Skull 

 (type): occipito-nasal length, 42.7; zygomatic breadth, 25.9; mastoidal 

 breadth, 18.4; least interorbital breadth, 12; length of nasals, 14.2; al- 

 veolar length of maxillary toothrow, 8.2. 



Remarks.— This race is most nearly related to castanurus from which it 

 may always be distinguished by its paler tail. In winter pelage caryi is 

 decidedly grayer dorsally than castanurus; in summer pelage the differ- 

 ences in color apparently are less, but only a single adult in full pelage 

 has been examined and that from a region where we might expect inter- 

 gradation to occur. Certain immature specimens of caryi bear a marked 

 resemblance to certain specimens of trepidus from Nevada, but compari- 

 son of typical adults shows that caryi differs from that form in having the 

 shoulders and sides of the head darker — tawny instead of ochraceous. 



Specimens examined. — Total number, 11, from localities as follows: 

 Wyoming : Fremont Peak, 3 ; Lake Fork, Wind River Mts. , 2 ; Bull Lake, 

 Wind River Mts., 1; Jakey's Creek, 5 miles south of Dubois, 3; Kendall 

 (12 miles northwest), 1; Jackson, 1. 



