396 MURIDAE—DICROSTONYX 
inter-orbital region. The auditory bullae are not enlarged or 
particularly spongy. The anterior edges of the squamosals 
give off very characteristic, peg-shaped, post-orbital processes. 
The characteristic pattern 
of the cheek-teeth has been 
described on p. 388 (Fig. 55). 
The infolds on the opposite 
sides being about of equal 
depth, the dentine-spaces are 
of nearly equal size on each 
side. The tooth-rows are 
Fic. 58.—SKULL OF Dicrostonyx (life size). nearly parallel, and there is no 
Drawn by M. A. C. Hinton. noticeable foramen behind the 
alveolus of 772s. 
Dicrostonyx is now confined to circumpolar regions, where 
D. torquatus' ranges from the eastern shores of the White Sea 
probably throughout arctic Siberia, and D. udsonzus (Pallas),* 
or other species, are found throughout the arctic regions of 
America and north through the islands of the Polar Sea, where 
they are sometimes innumerable, through Grinnell and Grant 
Lands to beyond 83° N. lat. on the north-west coast (Aldrich). 
In Greenland, D. grenlandicus (Traill, Scoresby’s Journal 
Voyage Northern Whale Fishery, 1823, 417) is found from the 
extreme northern point in about 83° N. along the entire coast, 
south-west to about 81° N. in Hall’s Land, and south-east to 
69° N. (Feilden MS.). Feilden (Quart. Journ. Geol. Soc., 1878, 
566) found its remains in post-pliocene beds of Grinnell Land, 
at an elevation of at least 300 feet above present sea-level, and 
hence argues that it is not a recent immigrant to Greenland. 
A southern species, D. unalescensis of Merriam, occurs at 
Unalaskah, in about 54° N. lat. 
The genus is known as a fossil from France (Puy de Déme, 
and Bréche de Coudes, Allier ; described by Pomel as Avwecola 
[Myolemmus| ambiguus, Ann. Sct. de 0 Auvergne, xxv., 1852, 
363; first correctly identified by Hensel in 1855, later by 
Forsyth Major, A¢tz. Soc. [tal. Sez. Nat., xv., 1872, 111, pl. 2); 

1 Mus torquatus, Pallas, Nove Species Quad e Glirium, 1779, li., 205, described 
from the arctic regions of the river Obi, Siberia. 
2 Of. cit., 1779, ii., 208, described from Labrador. 
