ARVICOLA 477 



Asia Minor to Northern Palestine (Tristram), west and north 

 Persia, and the Altais. They ascend to about 4500 feet in the 

 Alps and Jura (Fatio). The relationships of east Asiatic forms 

 have not yet been worked out, and it is not known if they 

 really belong to the genus Arvicola. Microtus calamorum of 

 Thomas, described from reed-beds at Nanking, seems to be 

 allied to the North American sub-genus Aulacomys, which 

 in external form represents Arvicola, but has the enamel- 

 pattern of Microtus ; the single species inhabits boreal zones 

 in mountains from Alberta south to Oregon. 



Distribution in time:— Hinton finds small unidentified species 

 q{ Arvicola m the middle Pleistocene of . Grays Thurrock and 

 Ilford, in which they appear to have represented Mimomys of 

 previous horizons. The genus is not again encountered until 

 the Ightham horizon, in which A. abbotti (Hinton, Ann. and 

 Mag. Nat. Hist., July 1910, 34) is numerous. This is 

 undoubtedly a member of the scherman group, differing from 

 existing species in its larger size and more extreme fossorial 

 specialisation, as shown especially in the straightened incisors, 

 sloping occiput, and greatly reduced inter-parietal. The genus 

 may have owed its survival to the fact that, after the disappear- 

 ance of Mimomys, it had no competitors, and had nothing to 

 fear from subsequent immigrations, which seem to have 

 caused the extermination of the older forms of Evotomys and 

 of Chionomys. 



Geographical variation: — Miller recognises seven European 

 species, of which A. amphibius, the British Water Rat, is 

 described below. A. sapidus of Miller, of the entire Iberian 

 Peninsula and north through the Pyrenees at least to Garonne, 

 France, is an aquatic form, most nearly allied to and resembling 

 A. amphibius, but with broad nasals. A. terrestris (Linnaeus) 

 of Skandinavia, and eastwards at least into Russia, the Caucasus 

 and Elburz Mountains, is smaller than A. amphibius, with 

 yellower cheeks and skull slightly but evidently modified for a 

 fossorial existence ; the rostrum and occiput tend to be 

 obliquely truncate, and the inter-parietal subquadrate in outline ; 

 the teeth are rather heavy, the upper incisors projecting, the 

 roots oim^ and m^ not forming protuberances as in A. amphibius. 

 A. italicus (Savi) of Italian Switzerland and Italy, at least to 



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