426 MURID^— 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 {M. innuitus of Merriam) ; St Matthew and 

 Hall Islands, Bering Sea {^M. 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, i, 72, based on Microtus terrestrisoi 

 Schrank = i1/«jarz/a& of Pallas; Lataste, Ze Naturaliste, 15th October 1883,348 

 (sub-genus) ; Miller, N. 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 Arvicola, a name 

 formerly used to include all "voles," there can be no doubt as 

 to the use of the name Microtus for the present genus. The 

 full synonymy may be found in Miller's Catalogue. 



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 slighdy 

 larger on the hind feet. The soles are moderately hairy, and 

 there are six plantar pads, of which one may be rudimentary. 



The mammse 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 



