1903.] Allen, Mammals from Northern British Columbia. 54 * 



having suckled young, or show by their worn teeth that 

 they were fully adult. As of interest in showing the wide 

 range of variation in size and proportions in breeding females, 

 the collector's measurements of 40 specimens, all from Tele- 

 graph Creek, and including all of the breeding females in the 

 series of 265 specimens, are tabulated below in the order of 

 size, from which it will be seen that the total length ranges in 

 old adults with well-worn teeth from about 180-190 mm., 

 with the tail length ranging from about 82 to nearly 90; while 

 the young females, with generally wholly unworn teeth and 

 many of them still in the pelage of immaturity, range from 

 about 165 to 175, with a tail length of from about 72 to 80. 

 It will also be noted that the ratio of tail length to total length 

 is considerably higher in the larger and older specimens than 

 in the younger and smaller ones, ranging from about 44 to 48 

 in the former and 42.5 to 46 in the latter. It thus appears 

 that the length of the tail, as perhaps would be expected, in- 

 creases more than the length of the head and body between the 

 period of breeding age and complete maturity or old age. 



An examination of the skulls of these specimens shows that 

 while this wide range of variation in size may be referred 

 in large part to age, the element of individual variation 

 also plays an important part, since one of the largest speci- 

 mens in the series has the teeth unworn and the bones of the 

 skull not firmly united, while on the other hand, several of the 

 smallest specimens have the teeth greatly worn and the skull 

 sutures firmly closed. 



There is a much smaller proportion of adult males in the 

 collection than of adult females, but so far as the material 

 goes, there is no appreciable sexual difference in size. 



The type locality of Peromyscus arcticus was Fort Simpson, 

 on the Mackenzie River, about half way between Fort Liard 

 and Fort Norman. Fortunately the American Museum col- 

 lection contains a small series from each of these points, and 

 also from Hell Gate and Telegraph Creek, taken by Mr. 

 Stone in 1897 and 1898, numbering altogether about 30 speci- 

 mens. These, with the collection now under special notice, 

 represent the species by specimens taken in April, May, July, 



