THE MOUSE TRIBE. 



129 



the sides of the hinder part of the skull are completely roofed over with bone, as 

 in a turtle. This Rodent inhabits the district of Shoa, and is doubtless arboreal, 

 although nothing definite is known of its habits in a wild state. 



THE YOLES. 

 Genus Microtus. 1 



The voles, together with their near allies the lemmings and the musquash, 

 constitute a group closely allied to the Cricetines, but distinguished by the peculiar 

 character of their molar teeth. Indeed, the voles and their allies are evidently 

 nothing more than a specialised modification of the 

 Cricetine type, and it is more as a matter of convenience 

 than from any well-founded distinctive characters that 

 they are placed by themselves in a distinct subfamily. 

 The whole group is characterised by the molar teeth being 

 usually rootless or with imperfect roots, and composed of 

 two longitudinal rows of alternately-arranged triangular 

 prisms. These prisms, as shown in the accompanying 

 figure, decrease in number from the first to the third 

 tooth in each jaw, but are variable in number in the 

 different species, and thus form a valuable aid in their 

 discrimination. The tail of the voles is either short or of 

 moderate length; and these Rodents are distinguished 

 from the true rats and mice not only by this character, CROWN-SURFACE OF THE URPER 

 but likewise by their more corpulent form, their smaller AND LOWEB M LAR TEETH 



, A, . , , OF THE CHINESE VOLE. 



eyes and ears, their more obtuse muzzles, and proportion- (From Thomas.) 

 ately shorter limbs. The subfamily has a wide distribution 



in the Northern Hemisphere, but is quite unknown in Asia south of the Himalaya, 

 in the Malayan region, and in Africa and South America. It is connected 

 with the Cricetine subfamily by a North American genus known as Phenacomys, 

 in which the molar teeth are furnished with roots. 



The water-vole, or, as it is commonly termed, the water-rat 

 (Microtus amphibius), may be taken as a typical example of the 

 widely-distributed group of voles, of which there are about half a hundred species, 

 ranging from Britain through Europe to China, and thence eastwards to North 

 America. The genus is sufficiently characterised by the molars being rootless and 

 the soles of the feet naked. 



From its diurnal habits and wide distribution the water-vole is one of the best 

 known of the indigenous British mammals. In size it agrees approximately with 

 the brown rat, the length of the head and body being about 8J inches, and that 

 of the tail slightly more than half as much again. The fur is dense and shining, 

 and of a full reddish brown colour mingled with grey above and yellowish grey 

 below. The feet are not webbed, and the tail is hairy. The number of the prisms 



1 The name Arvicola has been commonly applied to the voles, but by the rules of zoological nomenclature it 

 has had to give place to Microtus. 

 VOL. III. 9 



Water-Vole. 



