396 MURID.E— 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 



Fig. 58.-SKULL OF Dicrostonyx (life size), nearly parallel, and there is no 

 Drawn by M. A. c. Hinton. noticeable foramen behind the 



alveolus of m^. 



Dicrostonyx is now confined to circumpolar regions, where 

 D. torquaius^ ranges from the eastern shores of the White Sea 

 probably throughout arctic Siberia, and D. hudsonius (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. grcenlandicus (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 D6me, 

 and Br^che de Coudes, Allier ; described by Pomel as Arvicola 

 \Myolemmus'\ ambiguus, Ann. Sci. de P Auvergne, xxv., 1852, 

 363; first correctly identified by Hensel in 1855, later by 

 Forsyth Major, Atti. Soc. Ital. Sci. Nat., xv., 1872, iii, pi. 2); 



' Mus iorguatus, Pallas, Nova Species Quad e Glirium, 1779, ii., 205, described 

 from the arctic regions of the river Obi, Siberia. 

 2 Op. cit, 1779, ii-, 208, described from Labrador. 



