106 Proceedings of the Biological Society of Washington. 



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

 decidedly smaller than that of cineraacenB 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 doraally 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 diflers 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. 



