520 Life-histories of Northern Animals 



GENERAL "Similar to Microtus pennsylvantcus, hut much smaller, 



ACTERs with slenderer feet and tall, and paler colour. 

 COLOUR ^^ Summer pelage: Upper parts, yellowish bister with 



numerous dark-brown or black-tipped hairs; 

 sides of nose and hairs In front of ears more 

 decidedly yellowish; belly, white or rarely tinged 

 with buffy, sometimes dusky during the molt; 

 feet, silvery gray; tall, bicolour, blackish above, 

 whitish below. Winter pelage: Paler than in 

 FiG.iso^Righthmd- summer, yellow on ears and nose more eoli- 

 th ^I^^Zr'"'- splcuous. Toung: Paler and not so sooty as 



Uife size) '■ ° _ •' 



young pennsylvanicus. 

 CRANIAL Skull, not much arched and rather flat-topped, slender 



CHAR- 11^ 



ACTERS but sharply ridged In adults; audltal bullae, large and smoothly 

 rounded; palate, flattened In Immature specimens, becoming 

 higher with deep lateral pits In adults; dentition, as In pennsyl- 

 vanicus. Except for the larger bullae and a few characters of 

 minor weight, the skull of drummondi Is a miniature of the 

 skull of pennsylvanicus. 



MEASURE- "Average of 6 adult males and females from Muskeg 

 Creek, Alberta: Total length, 145 (5I-I Inches) ; tail vertebrae, 39 

 (lif inches); hind-foot, 17.8 (H Inch); largest specimen from 

 Muskeg Creek: 160; 41; 18 (6t^^; if; \\ inches); skull (No. 

 81487, 5 ad. same locality), basal length, 23 (f| Inch); nasals, 6 

 (i^Inch); zygomatic breadth, 14 d^^Inch); mastoid breadth, 11 

 (tV inch); alveolar length of upper molar series, 6 (i\ inch).'* 



The following races are recognized: 



pennsylvanicus Ord. The typical form. 



drummondi Aud. and Bach. Much smaller, slen- 

 derer, and paler than the type. 



nigrans Rhoads. Larger and darker. 



acadicus Bangs. Smaller and paler than the type. 



modestus Baird. Size of type, but paler, yellower, and 

 with shorter tail. 



fontigenus Bangs. Smaller than type, with short, 

 wide skull. 



