ABVIOOLA 725 



Interparietal tending to be somewhat ligulate in 

 outline; skull representing the extreme of 



fossorial adaptation A. schermfm, p. 744. 



Colour dark brown, the tail usually blackish 

 throughout ; habits both aquatic and fossorial 

 (Northern central Europe from southern 

 Germany to the Baltic and from Belgium 



eastward) a. s. scherman, p, 745. 



Colour light yellowish brown, the tail usually 



bicolor or bufiy; habits mole-like, strictly 



fossorial. 



Anterior loop of m l short and wide ; auditory 



bullae usually somewhat flattened (Alps 



and their immediate neighbourhood) A. s. exilus, p. 746. 



Anterior loop of m l long and narrow ; auditory 

 bullae evenly inflated (Pyrenees and their 



immediate neighbourhood) A.s. monticola, p. 749. 



Interparietal tending to be quadrate in outline; 

 skull less extremely fossorial in form. 

 Molars relatively weak ; underparts with con- 

 spicuous rusty wash which usually spreads 

 noticeably on sides of head (Norway and 



Sweden) A. terrestris, p. 738. 



Molars relatively heavy; underparts with at 



most an ochraceous wash which rarely 



spreads noticeably on sides of head. 



General colour strongly yellowish, the back 



with little if any clouding of black (Central 



Italy) A. musignani^.li^. 



General colour dark brown, the back with 

 noticeable clouding of black. 

 Underparts slaty, washed with yellowish 

 brown (Italian Switzerland and north- 

 ern Italy) A. italicus, p. 740. 



Underparts slaty, washed with whitish 



(Bosnia and Roumania) A. illyricus, p. 741. 



ARV1COLA AMPHIBIUS Linnseus. 

 (Synonymy under subspecies.) 



Geographical distribution. — Great Britain. 



Diagnosis. — Size large (head and body about 200 mm., tail 

 about 110 mm., hind foot usually 30 to 34 mm., condylobasal 

 length of fully adult skulls, 40 to 44 ■ 6 mm.) ; tail somewhat 

 more than half as long as head and body ; colour above dark 

 brown, blackening along back, the sides not decidedly yellowish, 

 the cheeks not contrasted with surrounding parts ; skull not 

 fossorial in form, the rostrum and occiput tending to be squarely 

 truncate (vertically), the upper incisors not unusually pro- 

 jecting ; nasals at widest region conspicuously narrower than 

 rostrum ; roots of m^ and m 2 forming evident protuberances on 

 lower surface of mandible in old individuals ; habits strictly 

 aquatic, never mole-like. 



External characters. — General form heavier and more robust 

 than in the house rat, the tail relatively shorter and head 



