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 Avvicola. Mucrotus calamorum of 
Thomas, described from reed-beds at Nanking, seems to be 
allied to the North American sub-genus Axzlacomys, which 
in external form represents Avvzcola, but has the enamel- 
pattern of A/zcrotus ; the single species inhabits boreal zones 
in mountains from Alberta south to Oregon. 
Distribution in time :—Hinton finds small unidentified species 
of Avvicola in the middle Pleistocene of Grays Thurrock and 
Ilford, in which they appear to have represented A/zmomys of 
previous horizons. The genus is not again encountered until 
the Ightham horizon, in which A. addotte (Hinton, Ann. and 
Mag. Nat. ffst., 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 A/zmomys, it had no competitors, and had nothing to 
fear from subsequent immigrations, which seem to have 
caused the extermination of the older forms of Zvotomys and 
of Chzonomys. 
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. amphabius, but with broad nasals. A. terrestris (Linnzus) 
of Skandinavia, and eastwards at least into Russia, the Caucasus 
and Elburz Mountains, is smaller than A. amphibtus, 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 of #, and m, not forming protuberances as in 4. amphabius. 
A. ttalicus (Savi) of Italian Switzerland and Italy, at least to 
VOL, II. 2H 2 
