LHE 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 VOLES. 
Genus MWicrotus. 
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-surrace OF THE UPPER 
but likewise by their more corpulent form, their smaller = “4” SOWBR MOPAR TEETH 
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 8} 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 
<P 
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+4 
CHIN 

Water-Vole. 
1The 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.—g 
