158 MICROTINiE 



Characters.- — Size rather large ; hind-foot to 24 mm. ; condylo- 

 basal length of skull to 32 mm. Variable cheek-teeth {m}, nfi, 

 and m^ somewhat simplified ; m^ and m^ each lacking a postero- 

 internal vestigial angle and with the posterior wall of the hinder 

 inner triangle more or less reduced ; m^ without anterior vestigial 

 angles. Upper parts of adults in summer pelage nearly uniform 

 bulfy grey ; with a median blackish line from the nape to the tail, 

 not sharply defined ; ear-tufts, sides of body and throat buff ; 

 belly grey. 



Colour of adults m summer. — General tone of upper parts, 

 including the head, varying between buify grey and clear grey, 

 produced by the mixture of three kinds of hairs, some grey-tipped, 

 others with dusky tips and yellowish subterminal bands, and still 

 others longer and entirely black, the precise hue depending 

 largely upon the development of the yellowish subterminal ring 

 in the second sort of hairs. A black spinal line extends from the 

 nape to the tail, but is not sharply defined. Ear on each side 

 surrounded by an indistinct greyish patch ; while each ear-tuft 

 is composed of tawny hairs. Throat collar represented by a wash 

 of tawny connecting the axilla? and sometimes continued back- 

 wards on the chest in the middle line. A paler tinge of tawny 

 along the flanks and about the anus. A buffy spot on each side 

 of the nose and around the eye. Tail like the back, or with a 

 tuft of long grey hairs. The young in summer are like the adults 

 but darker; the spinal stripe extends to the point of the nose 

 and is more sharply defined ; the throat collar is very indistinct. 



Skull. — With dorsal contour rather more convex and less 

 flattened from before backwards than in other recent species; 

 nasals relatively long; interparietal frequently articulating 

 laterally with the squamosals ; presphenoid rather broad. 



Cheek-teeth. — m^ and m'^ with the hinder wall of the postero- 

 internal triangle in each tooth reduced, straight or convex instead 

 of being concavely curved, its thick enamel more or less atrophied ; 

 no postero-internal vestigial angles, m^ without any trace of 

 the anterior vestigial angles present in all other known species 

 (Fig. 72, 4). 



For external and cranial measurements, see tables at end of 

 volume. 



FOSSIL SPECIES. 



Fossil remains of Dicrostonyx occur abundantly in the late 

 Pleistocene deposits of Europe, and have been found in deposits 

 of a similar age in northern and central Asia ; but hitherto none 

 have been detected in North America. 



Pomel was the first to pay attention to these remains in 

 Europe, and his excellent description ^ of some lower jaws, from 

 the Breche de Coudes, in the Auvergne, upon which he based his 



» Pomel, Catalogue Methodique, 1853, p. 27. 



