426 MURIDA:—MICROTUS 
Although still imperfectly known, the genus includes a 
bewildering number of species, which, with their sub-species, 
probably outnumber all other members of the sub-family 
united. These are widely distributed in boreal and transitional, 
less frequently in arctic or subtropical zones, from ocean to 
ocean in North America, with Newfoundland, and south to 
southern Mexico; in Eurasia from the Outer Hebrides to 
Kamchatka ; and south to Portugal, Central Spain, the Medi- 
terranean coasts of France, Northern Italy, the central portions 
of the Balkan Peninsula, Asia Minor, Northern India, and 
the island of Kiushiu, Japan. 
The genus probably originated in Asia and crossed to North 
America by the Bering Sea route, leaving traces of its presence 
in St Lawrence (JZ. zunuztus of Merriam); St Matthew and 
Hall Islands, Bering Sea (17. abbreviatus of Miller). 
The genus having been subdivided, its characters may be 
given under the sub-genera. 
SuB-GENUS MICROTUS. 
1798. Microtus, F. v. P. Schrank, Fauna Boica, 1, 72, based on Microtus terrestris of 
Schrank= dZus arvalzs of Pallas; Lataste, Le Naturaliste, 15th October 1883, 348 
(sub-genus) ; Miller, V. Amer. Fauna, No. xii., 23rd July 1896, 62 ; and Catalogue, 
1912. 
Synonymy :—Owing to difficulties of identification and classi- 
fication, the synonymy is long and complicated; but, since the 
segregation of the Water Rats in the genus Avvico/a, a name 
formerly used to include all “voles,” there can be no doubt as 
to the use of the name JZzcrotus for the present genus. The 
full synonymy may be found in Miller’s Ca¢alogue. 
These mice are sedentary grass-feeders of much narrower 
habits than the Bank Mice. They are neither climbers nor 
specially modified’ for a subterranean existence, in either fur, 
which is never dense or mole-like, or claws, which are slightly 
larger on the hind feet. The soles are moderately hairy, and 
there are six plantar pads, of which one may be rudimentary. 
The mammz are eight, as in Evotomys. 
The skull is ridged and angular; the inter-orbital region 
narrow ; the temporal ridges well developed. The bony palate 
(Fig. 60, B, p. 401) terminates posteriorly in a median ridge 
