714 



in M. agresiis. Ear rather large, appearing distinctly above 

 surrounding fur and extending nearly or quite to eye when laid 

 forward ; meatal lobe well developed, high, its margin evenly 

 rounded. Muzzle essentially as in M. agrestis. Feet as in 

 M. agrestis, but posterior plantar tubercle larger than those at 

 base of digits. Tail about half as long as head and body, the 

 hairs not entirely concealing the annulations, of which there are 

 about eighteen to the centimeter at middle ; pencil inconspicuous. 

 Fur full, soft and loose. Mammae : j> 2 — 2, i 2 — 2 = 8. 



Colour. — Upper parts smoke-grey, strongly washed with bister 

 on back, and usually tinged with pale buff along sides ; under- 

 pays dull white, irregularly clouded by the slaty under-colour ; 

 feet and tail whitish, the tail usually (in about two-thirds of the 

 skins examined) tinged with brown above though never sharply 

 bicolor. 



Skull. — The skull is larger than that of Microtus agrestis 

 agrestis, its general form broader and more depressed, the dorsal 

 surface much less marked by ridges for muscle attachment, and 

 the auditory bullse more developed. Dorsal profile nearly flat from 



lachrymal region to lambda, or 

 with a faint concavity in inter- 

 orbital region and equally slight 

 convexity over middle of brain- 

 case* ; nasals sloping forward at 

 an evident though slight angle 

 (about 15°). Occiput sufficiently 

 oblique for the condyles to be just 

 visible when skull is viewed from 

 above. Ventral profile with no 

 special peculiarities ; contrast be- 

 tween occipital depth and that 

 of rostrum evident but less pro- 

 nounced than in the European 

 members of the sub-genus Micro- 

 tus. Brain-case large relatively to 

 general size of skull, its outline 

 when viewed from above broadly 

 ovate, wider anteriorly than pos- 

 teriorly ; postorbital processes small and inconspicuous, producing 

 no very noticeable break in contour of brain-case ; ridges along 

 outer portion of parietals scarcely visible except in extreme old 

 age, and never becoming conspicuous ; lambdal crest represented 

 by extreme outer portions only, these much less developed than in 

 M. agrestis ; interparietal relatively smaller than in Jlf. agrestis, 

 its area scarcely more than half that of parietal, its form not 

 peculiar (antero-posterior diameter, exclusive of median projection, 

 slightly less than half transverse diameter). Depth of occiput 

 when viewed from behind barely more than half height, the 

 * Somewhat exaggerated in fig. 148. 



FIG. 148. 

 Microtus nivalis. Nafc. size. 



