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, Geo/, Mag., March 1901, 
to1-106. Hoe Grange Quarry, Longcliffe, near Brassington, Derbyshire, Arnold- 
Bembrose and Newton, Quart, Journ, Geol. Soc., 28th Feb. 1905, 43-64. Langwith 
Cave, Derbyshire, Mullins and others, Journ. 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 Arvicolide, Proc. Zool. Soc., 
London, 16th June 1874, 460-471.] 
[GENUS DICROSTONYX} 
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 ZLemmus, 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 
1 Extinct in Britain. Dzcrostonyx, Gloger, 1841, based probably on Mus hudsonius 
of Pallas, from Labrador, antedates Cumiculus, Coues, 1877, which latter is also 
preoccupied (see above, p. 172.) 
