48 THE BRITISH MAMMALS : THEIR GENERA AND SPECIES. 



the back. The characteristic beak is rather broad at the base, thereby 

 differing from that in some of the other species of the genus, in one 



SOWERBY'S WHALE. 

 (Mesoplodon bidens.) 



of which the strap-shaped teeth grow to such a size, curving in- 

 wards at the point, as to meet over the beak and prevent the mouth 

 from fully opening. 



Microtus. Plate xiii. RODENTIA. 



43. agrestis, FIELD VOLE. Head and body less than 6 inches; 



greyish above ; teeth prisms 5 -^- 6 - 



44. amphibius, WATER VOLE. Head and body more than 6 inches ; 



brownish above ; teeth prisms 5_4_* 



7 5 3 



45. glareolus, BANK VOLE. Head and body less than 6 inches; 



chestnut above ; teeth prisms ^- 5 



7 3 3 



The Voles have one pair of incisors and three pairs of molars in each 

 jaw, and no other teeth. The molars are characteristic, each tooth 

 consisting of two short series of triangular prisms alternately 

 placed, the number of prisms differing in each species. In all 

 cases the head is large, the muzzle rounded ; the ears and eyes 

 are small, the limbs and tail short, and the build generally is 

 heavier than that of the rats and mice. 



The Field Vole is greyish brown above and whitish below, 

 darker on the feet. The soles are bare, and on the hind pair are six 

 pads. The head and body measure about four and a half inches ; the 

 tail, which is hairy, is a third of that length. The teeth have no roots. 

 In the upper jaw the third molar has six prisms, the first and second 

 only five: in the lower jaw the third has three prisms, the second five, 

 and the first nine. This is the Vole that causes so much destruction to 

 farms and gardens. It seems to confine its attentions to cultivated 

 land, and is rarely found in woods. It feeds on everything vege- 



