DICROSTONYX 395 



and that its passage between the Old and New Worlds was by 

 way of Bering Strait. 



The principal original references to the ossiferous caves or fissures mentioned in 

 the articles on lemmings are as follows : — 



Ightham Fissures, Valley of the Shode, Kent, Abbott and Newton, Quart. Journ. 

 Geol. Soc, 1st May 1894, 171-209; Newton, Journ. cit, August 1899, 419-429. 

 Wye Valley Cave, Forest of Dean, Gloucestershire, Bate, Geol. Mag., March 1901, 

 101-106. Hoe Grange Quarry, Longcliflfe, near Brassington, Derbyshire, Arnold- 

 Bembrose and Newton, Quart. Journ. Geol. Soc, 28th Feb. 1905, 43-64. Langwith 

 Cave, Derbyshire, Mullins and others, /oarw. Derby Arch, and Nat. Hist. Soc, 1913. 

 Dog Holes, Warton Crag, Lancashire, Jackson, Lancashire Nat., Nov. 1909, 227- 

 229 ; Feb. 1910, 323 ; March 1912, 420-422. Kesh caves, Co. Sligo, Ireland, Scharff, 

 Coffey, Cole, Ussher and Praeger, Trans. R. Irish. Acad., Sept. 1903, xxxii., B. iv., 

 171-214. See also Blackmore and Alston, On Fossil Arvicolidce, Proc. Zool. Soc,, 

 London, i6th June 1874, 460-471-] 



[Genus DICROSTONYX.i 



The Banded or Arctic Lemmings are less specialised in 

 dentition and skull than the true lemmings, but much more so 

 in external characters, thus enabling them to exist in higher 

 latitudes. Some, at least, of the species whiten in winter. The 

 external ears are quite rudimentary. The hands undergo 

 remarkable seasonal changes. The thumbs are very small, and 

 their nails minute ; the claws of the two middle digits in 

 summer resemble those of Lemmus, but in winter they are 

 greatly enlarged in conformity with the subterranean life of the 

 animal at that season ; after attaining a maximum, portions of 

 them are shed somewhat like the horns of some ungulates ; the 

 claws of the second and fifth digits are large, but not peculiar 

 in form. The hind feet, which carry several minute pads near 

 the bases of the claws, are very broad, the proportions of 

 length to breadth being about as two to one. 



The skull resembles that of Lemmus, but is smaller and 

 more lightly built, with zygomata less broadly bent and 

 expanded, lighter and more slender rostrum, and pterygoids 

 proportionately longer. The temporal ridges never unite, and 

 there is consequently a noticeable longitudinal furrow in the 



' Extinct in Britain. Dicrostonyx, Gloger, 1841, based probably on Mus hudsonius 

 of Pallas, from Labrador, antedates Cuniculus, Coues, 1877, which latter is also 

 preoccupied (see above, p. 172.) 



