174 NORTH AMERICAN FAUNA. [no. 27. 



With the rather limited amount of material available, I am unable 

 to discover tangible cranial differences between S. sdbrinus and 

 alpinns. 



In addition to the Elk River specimens, Richardson mentioned 

 having received others from the south branch of the Mackenzie 

 [Liard ] ; ° and Rhoads has recorded two specimens from Fort Liard 

 as S. <il i>ini(x. h Ross recorded Pteromys alpinus as rather rare in the 

 mountain ranges of Liard River.'' 



Peromyscus arcticus (Mearns). Arctic White-footed Mouse. 



This familiar species is abundant throughout the region north to 

 the lower part of Grandin River and Fort Norman. During the 

 three seasons spent in the north we collected a very large series, com- 

 prising specimens from the following localities: Alberta: 40 miles 

 north of Edmonton ; Athabaska River, 5 and 30 miles above Atha- 

 baska Landing; Swift Current, and several points between there and 

 Pelican Portage; Pelican River; Grand Rapid; Bride Rapid; 

 Crooked Rapid; Cascade Rapid; Mountain Rapid; Fort McMurray; 

 Fort Chipewyan; Slave River, 10 and 25 miles below the Peace; 

 Smith Landing. Mackenzie: Fort Smith; Fort Resolution; Trout 

 Rock (25 miles south of Fort Rae) ; Fort Rae; lower Grandin River; 

 Fort Providence; Willow River (near Fort Providence) ; Fort Simp- 

 son; mountains at mouth North Nahanni River; Fort Wrigley; and 

 Fort Norman. A large series from Fort Simpson, the type locality of 

 P. arcticusf on comparison with the rest of the series, shows that the 

 species remains remarkably constant over a very large area. The 

 principal variation appears in the series from the upper Athabaska. 

 individuals of which have much longer tails, on the average, than 

 typical specimens from farther north. In some respects these show a 

 tendency toward Peromyscus oreas, but the measurement of the hind 

 foot falls far short of the same dimension in typical oreas, and the 

 specimens seem properly referable to arcticus. Ten adults from Fort 

 Simpson average: Total length 102.2, tail vertebra 72.2. hind foot 

 20; five from near mouth of North Nahanni River, 171, 77, 20.5; four 

 from Fort Norman. L65, 75.5, 20; ten from Fort Providence, 175, 00, 

 20; ten from Fort Rae, 168.7, 71.4, 20; ten from Fort Resolution, 101, 

 71.8, 20.3 ; ten from Fort Smith, 173.2, 70.5, 20 ; ten from Fort Chip- 

 ewyan, 107.7, 74.8, 20; ten from 30 miles above Athabaska Landing, 

 173, 83.3, 20. The tendency toward elongation of the tail in the 

 white-footed mice of the upper Athabaska is well shown in this last 

 series. 



" Fauna Boreali-Americana, I, p. 1!>~>, 1829. 



6 Proc. Acad. Nat. Sci. Phila.. 1897, p. 320. 



''Can. Nat. and Geol., VII, p. 140. 1862. 



d Mearus, Bull. Am. Mus. Nat. Hist., II, p. 285, L890. 



