as Enemies of Mankind. 



53 



cealing the scaly annulations. Anterior lower molar with 

 only three closed triangles (Fig. 4 C). 



1. Size larger (head and body about 200 mm. ; tail about 

 110 mm. ; hind-foot usually 32 to 35 mm.). General colour 

 brown. 



Common Water Vole, Arvicola am^hihius amidhihius. 

 (Distributed throughout England and Lowlands of 

 Scotland.) 



2. Size smaller (hind-foot 30 to 32 mm.). General colour 

 black. 



Highland Water Vole, A. amphibms reta. (Distributed 

 in the Highlands of Scotland.) 



In general our Voles are distinguished from our true Eats and 

 Mice by their heavier build, blunter muzzles, smaller eyes, shorter 

 ears, and comparatively well haired tails ; the females of each 

 species have eight mammae, two pairs on the chest, two pairs in 

 the groin. The Bank Vole is our most primitive species ; its 

 rooted teeth have been inherited with little change from the more 

 generalized ancestors of the sub-family; its diet is of a more 

 omnivorous character than is that of the more highly developed 

 voles. Our species of Microtus are highly specialized as feeders 

 upon grass and coarse herbage. The Water Voles are similarly 

 addicted to a hard diet ; and they are, moreover, highly developed 

 for their aquatic existence. 



The Murinae are represented in Britain by four genera ; 

 these and their species may be distinguished as follows : — 



A. First and second upper molars with three tubercles on the 

 inner side when unworn (Fig. 5 A-B). 



a. Tail not prehensile, completely haired at the tip ; orifice 

 of ear not closed by a special valve. Mammae in females six, 

 one pair being on the chest, two pairs towards the groin. 



1. Size smaller (head and body about 95 mm. ; tail about 

 90 mm. ; hind-foot about 22 mm. ; ear 15 to 17 mm.). 



Long-Tailed Field Mouse, Apoclcmus sylvaticus. (Dis- 

 tributed throughout Great Britain and Ireland.) 



2. Size larger (head and body 100 to 115 mm. ; tail 105 to 

 125 mm. ; hind-foot 23 to 27 mm. ; ear 17 to 19 mm.). 



De Winton's Field Mouse, A. flavicollis njintoni. (Dis- 

 tributed through much of England.) 



