430 MURID^— AGRESTIS 



Distribution : — The Northern Grass Mouse ranges from the Outer 

 Hebrides, Scotland, and Skandinavia, at least to North-western 

 Mongolia, where the local form, M. a. mongol of Thomas, can only be 

 distinguished from true agrestis by its larger bullae ; there is also an 

 isolated colony — M. a. levernedii (Crespon) — inhabiting the Alps, 

 Jura, and neighbouring portions of Switzerland and France, with the 

 marshes at the mouth of the Rhone on the Mediterranean coast of 

 France. Although completely isolated geographically, levernedii is 

 not well differentiated from M. a. agrestis of Skandinavia, and can 

 only be distinguished by its longer and narrower skull, in which the 

 distance from the condyles to the back of the inter-orbital constriction 

 is usually greater than the zygomatic breadth, whereas in M. a. agrestis 

 these two dimensions are usually about equal. M. a. agrestis is, in 

 Skandinavia, chiefly, but not entirely, a lowland form ; it is one of the 

 most numerous mammals of Norway, being found on the cultivated 

 islands and ranging to the extreme north of the country at Lebesby 

 (Collett). 



In Britain it is confined to the Highlands of Scotland and the 

 western Scottish islands (but notably absent from Lewis), where it 

 occurs in five sub-specific forms. 



Distribution in time : — The species first appears in Britain in the 

 late pleistocene deposits of Ightham, Kent (see under M. a. neglectus). 



Description : — M. agrestis may be known amongst European species 

 by its moderate size (hind foot, i8 to 21 ; condylo-basal length of skull 

 in adults, 25 to 28-7 mm.), and especially by its in"', which has a well- 

 developed postero-internal triangle forming a third inner angle. 



In form and appearance, in which it is typical of its genus, it 

 differs chiefly from Evotoniys in its more robust, thicker build, less 

 conspicuous ears, shorter tail, and duller tints. 



The evenly rounded ears are hidden in the fur, and when laid 

 forward reach about half-way to the eyes ; the meatal lobes are well 

 developed and reach a height centrally of about 3 mm. The small 

 eyes are not prominent ; they lie nearer the muzzle than the base of 

 the ears. The tail is about one-third as long as the head and body. 

 The mouth is small. 



The hands and feet resemble those of Evotomys glareolus, but the 

 minute thumb is almost concealed dorsally by the relatively large nail, 

 and the hallux does not quite reach the base of digit two. 



In the tail the annulations are pronounced but slightly irregular, 

 their number about 20 to the cm. centrally ; they show through the 

 thin hairs, which, however, form a distinct terminal tuft. 



The skull is moderately broad, the ratio of zygomatic breadth to 

 condylo-basal length being from 55 to 60; the inter-orbital region 

 develops a distinct ridge in adults ; the length of the brain-case 



