430 MURIDA:—AGRESTIS 
Distribution :—The Northern Grass Mouse ranges from the Outer 
Hebrides, Scotland, and Skandinavia, at least to North-western 
Mongolia, where the local form, JZ. a. mongol of Thomas, can only be 
distinguished from true agvestés by its larger bullae; there is also an 
isolated colony—JZ, a. levernediz (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, /evernedzz is 
not well differentiated from J7. 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 JV. a. agrestis 
these two dimensions are usually about equal. JZ. 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 JZ. a. neglectus). 
Description :—J/. agrestis may be known amongst European species 
by its moderate size (hind foot, 18 to 21 ; condylo-basal length of skull 
in adults, 25 to 28-7 mm.), and especially by its 7z?, 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 Hvotomys 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 
