MAMMALS THAT GNAW. I03 



Closely allied to the ciioetines, of which they may be regarded as a 

 Epeeialised branch, the large group of voles are distinguished by iheir gener- 

 ally rootless, or imperfectly rooted molars being composed 

 of two longitudinal rows of alternating triangular prisms. The Vole Group 

 Externally they differ in most cases from the typical rats (Microlma:). 

 and mice by their heavier and less elegant form, less active 

 movements, smaller eyes, blunter muzzle, smaller ears, and shorter limbs and 

 tail. They are restricted to Europe, Asia north of the Himalaya, and North 

 America. An annectant form between tlie cricetines and typical voles is the 

 North American genua Fhe^iacomys, in which the molars develop roots. The 

 typical genus Microtus-, which includes nearly half a hundred species ranging 

 over Europe, Northern Asia, and North America, is sufficiently characterised 

 by its rootless molars and the naked soles of the feet ; the British forms being 

 the water-vole {M. amphibiics), the field-vole (M. agrestis), and the red, or 

 bank-vole (M. glareolus). Each of these is the representative of a distinct 

 sub-generic group, severally characterised by the number of prisms in the 

 molar teeth, and to which the names Paludicula, Agricola, and Evotomys have 

 respectively been applied. The extraordinary hordes in which some species 

 of land voles make their appearance at) cerlaui seasons, and the damage they 

 then inflict on agricultural produce, aro maiters of common knowledge. The 

 round tailed musk-rat of Florida, which has been regarded as constituting a 

 genus {Neofiber) by itself, is considered by Dr. Merriani to be not more than 

 a sub-genus of Microtus. Nearly allied la the true musk-rat. or musquash 

 (Fiber zibelhicus), of North America, which is the largest member of the 

 group, and measures nearly a foot in length to the root of the tad. Heavily 

 built, it is characterised by its broad head — which joins the body without any 

 well-defined neck, — short limbs, small eyes, ears nearly concealed in the thick, 

 beaver-like fur, and the rudimental first toe of the fore-foot ; the long tail 

 being laterally compressed, scaly, and sparsely haired. The general colour is 

 dark brown, tending to black on the back, and grey on the under-parts. 

 Both sexes have a gland secreting the musky substance from which the animal 

 derives its name. Although its toes are not webbed, the musk-rat is an 

 aquatic creature, feeding on a mixed vegetable and animal diet. Its fur is of 

 considerable value ; and the skull is very similar to that of Microtis. Another 

 distinct generic tj'pe is presented by the groove-toothed vole (Synaptomys) of 

 the United States, in which the upper incisors are grooved, while the external 

 form resembles that of the true voles, and the molars are like those of the 

 lemmings. The latter Rodents (Mijodcs), of which there is one Old World 

 and one North American species, differ from the voles by their heavier 

 build, the blunt convex head, very short tail and ears, the hairy soles of 

 the small feet, the bevelled upper incisors, and the pattern of the molar 

 teeth. 



The common lemming (M. lemimis), which measures about five inches in 

 length, and has yellowish-brown fur with darker spots, is remarkable for the 

 periodical migrations undertaken by its countless swarms ; these hordes pass- 

 ing over e\'ery obstacle in their course till they finally reach the sea, in 

 which they perish. Nearly allied to the last genus, the circumpolar 

 banded lemming (Cnniculus torquatus) may be easily distinguished by the 

 absence of external ears, the shortness of the feet, which are thickly 

 haired beneath, the rudimental first toe of the fore-foot, and the great 

 length of the claws of the third and fourth toes of the same. The molars 

 approximate to those of the voles, but the first in the upper jaw diifers 



