180 NORTH AMERICAN FAUNA. [no. 27. 



the specimens taken. Our specimens in this phase are quite uniform 

 in coloration, and differ from those in the red or normal phase mainly 

 in the color of the dorsal stripe, the sides and lower parts being prac- 

 tically normal. The dorsal stripe is slaty brown, in some specimens 

 very slightly tinged with reddish, and one taken 25 miles below the 

 Peace shows considerable red, and may be considered fairly inter- 

 mediate between the two phases. The series of dark-backed speci- 

 mens includes but one young one, a quarter grown individual from 

 Fort Smith. 



Bailey, under the name E. gapperi, records specimens taken by 

 Loring at Edmonton; St. Albert; Muskeg Creek; 15 miles west of 

 Henry House; and 15 miles south of Henry House, Alberta." These 

 specimens are not typical E. g. athabascce, but are here provisionally 

 included under this form. 



A specimen in the gray phase of color from Red [Deer] River, 

 south-central Alberta, has been recorded by Allen.'' 



Evotomys dawsoni Merriam. Dawson Red-backed Mouse. 



This fine species ranges throughout the Mackenzie region from 

 Great Slave Lake northward to the limit of trees. During our 

 investigations Ave collected a large series, comprising specimens from 

 the following localities in Mackenzie: Trout Rock (near Fort Rae) ; 

 Fort Rae; Grandin River; Lake Faber; Lake St. Croix; north of 

 Lake St. Croix; Lake Hardisty; near Leith Point, Great Bear Lake; 

 Fort Franklin; Fort Providence; Fort Simpson; mouth of Xahanni 

 River; Fort Norman; Fort Good Hope; and Fort McPherson. 



This species replaces E. g. athabascce, north of Great Slave Lake, 

 and no evidences of intergradation have been found. The difference 

 between the two is so striking that I instantly noted it when I took 

 the first specimen of E. dawsoni. In the latter the dorsal stripe is 

 much lighter and brighter and grades insensibly into the ochraeeous 

 of the face, cheeks, and sides. In E. g. athabascai from Fort Resolution 

 and southward, the face, cheeks, and sides are grayish, with scarcely 

 a tinge of ochraeeous, the face especially being strikingly different 

 in coloration. The skulls of E. <hiirx<>ni are conspicuously narrower 

 interorbitally, and have smaller bullae, than those of E. g. athabasvm. 



Eight adults from near Fort Rae average in measurements: Total 

 length 138, tail vertebra' 33.6, hind foot 18.3; ten from Lake St. 

 Croix, 131.3, 31.8, 1S.8; ten from Fort Franklin. 1-28.4, 31.4, 18.5; 

 ten from Fort Simpson. 120.4, 33.3. 18.5; eight from Fort Norman. 

 L32.7, 34. 18.6; eight from Fort Good Hope. 142, 35. 18.8; eight from 

 Fort McPherson, 133.7, 34.8, 18.0. The number of embryos recorded 

 in several instances varied from 2 to (>. 



"I'roc. Biol. Soc. Wash., XI. i». t24, L897. 

 6 Bull. Am. Mus. Nat. Hist., XII. i». 9, 1899. 



