660 



RODENTIA 



France, northern Italy, the central portion of the Balkan Penin- 

 sula, Asia Minor and northern India. 



Diai/uosis. — Principal characters as in the genus ; third upper 

 molar with three re-entrant angles on inner side ; skull with 

 brain-case narrow and high, or broader and more flattened, its 

 surface ridged and angular ; interorbital region narrow, the 

 temporal ridges well developed ; elements of posterior edge of 

 palate well detined. 



Hemarhs. — The sub-genus Microtus contains most of the 

 members of the genus. Twelve species are now known to occur 

 in western Europe. 



KEY TO EUROPEAN FORMS OF THE SUB-GENUS 2IICR0TUS. 



Second upper molar with two closed triangles on 



inner side M. agresiis, p. 662. 



Condylobasal length of skull in largest individuals 

 27 to 28-4 mm. 

 First upper molar with third inner triangle 

 usually present; miderparts heavily washed 



with wood-brown (Hebrides) M. a. exsul, p. 669. 



First upper molar with third inner triangle 

 usually absent ; underparts slightly or not 

 washed with wood-brown. 

 Brain-case relatively long, the distance from 

 condyle to back of interorbital constric- 

 tion decidedly greater than zygomatic 

 breadth (Alps and their immediate 

 neighbourhood ; marshes near mouth 



of Rhone) M. a. levernedii, p. 671. 



Brain-case relatively short, the distance from 

 condyle to back of interorbital constric- 

 tion about equal to zygomatic breadth 



(Scandinavia) M. a. agrestis, p. 668. 



Condylobasal length of skull in largest individuals 



24-6 to 26-6 mm. 



Auditory bulla small and flattened, its greatest 



diameter (from paroccipital process to tip 



of anterior spine) contained about 3^ times 



in condylobasal length of skull (Portugal 



and north-western Spain) M. a. rozianus, p. 680. 



Auditory bulla large and inflated, its greatest 

 diameter contained about 3 times in condy- 

 lobasal length of skull. 

 Condylobasal length of skull in largest indi- 

 viduals 25 to 26 mm. (England and 



southern Scotland) M. a. hirtus, p. 673. 



Condylobasal length of skull in largest indi- 

 viduals 25-4 to 26-6 mm. 

 General colour of upper parts darker, 

 usually with decided tinge of russet 



(Northern and central Scotland) ^[. a. neijlectus, p. 675. 



General colour of upper parts lighter, 



usually with no decided tinge of russet 



(West-central Continental Europe).... M. a. baillom, p. 672. 



Second upper molar with one closed triangle on 



inner side. 



First lower molar with three re-entrant angles 



on outer side M. ratticeps, p. 708. 



