662 RODENTIA 



largest skulls 26-6 to 27 "6 mm. 



(North Orkney Islands) M. sandayensis, p. 696. 



First lower molar \Yith anterior 

 outer re-entrant angle obso- 

 lete; back decidedly greyish ; 

 underparts scarcely tinged 

 with yellowish brown (Sanday 



Island) M.S. sa»rfa)/e»si«, p. 697. 



First lower molar with anterior 

 outer re-entrant angle usually 

 well developed ; back not de- 

 cidedly greyish ; underparts 

 strongly washed with yellow- 

 ish brown (Westray Island)... M. s. westriv, p. 698. 

 Largest skulls with condylobasal length less 

 than 27 mm. 

 Brain-case with occipital region noticeably 

 flattened ; skull in general tending to 



assume a fossorial aspect (Alps) M. inccrtus, p. 690. 



Brain-case with occipital region not notice- 

 ably flattened ; skull in general not 

 tending to assume a fossorial aspect. 

 Interorbital region much elevated, so 

 that dorsal profile of skull is strongly 

 convex (Asturias and Sierra de Gua- 



darrama) M. asturiatuis, p. 693. 



Interorbital region low, so that dorsal 

 profile of skull is slightly convex or 



nearly flat M. arvalis, p. 681. 



Skull narrow and rounded ; brain-case 

 so long that distance from condyle 

 to back of interorbital constric- 

 tion is greater than zygomatic 

 breadth (Roumania and southern 



Hungary) M. a. levis, p. 687. 



Skull broad and rather angular ; 

 brain-case so short that distance 

 from condyle to back of inter- 

 orbital constriction is at most 

 equal to zygomatic breadth. 

 General colour greyish or brownish, 

 the sides of body not conspicu- 

 ously huffy (Eastern Germany) M. a. dupHcatus, p. 686. 

 General colour a decidedly yellowish 

 brown, the sides of body con- 

 spicuously suffused with buff. 

 Size slightly smaller and colour a 

 little less yellowish (Central 



Europe) M. a. arvalis, 'p. 683. 



Size slightly larger and colour a 

 little more yellowish (Pyre- 

 nees) M. a. meridiainis, p. 686. 



MICROTUS AGRESTIS Linnjeus. 



(Synonymy under subspecies.) 



Geographical distribution. — Northern and central Europe from 

 northern Scandinavia to the Alps, Pyrenees, Galicia and Portugal, 

 and from England, Scotland and the Hebrides eastward. 



