3 H THE HOLARCTIC REGION. [CHAP. 



in America they enter the Sonoran region. As fossils, they appear 

 to be first known from the upper Pliocene Crag of England ; and 

 were thus probably evolved within the Holarctic region from the 

 more generalised cricetines at a comparatively late epoch. Nearly 

 allied are the lemmings (My odes), which are, however, a more 

 northern type, unknown in the Mediterranean sub-region, and 

 likewise in the Sonoran. Still more northern, and indeed circum- 

 polar in its range, is the banded lemming, which alone represents 

 a genus (Cuniculus) distinguished from the last by the absence of 

 external ears, the short and thick fur on the feet, the rudimentary 

 first toe of the fore feet, and the elongation of the two middle 

 claws of the same. The second of the two families peculiar 

 to the region is that of the picas, or tailless hares (Lagomyidce), 

 comprising small hare -like animals with short ears, of which 

 all the living forms are included in the single genus Lagomys. 

 While the majority of the picas are confined to the highlands 

 of Central Asia, some are found on the first snowy range of the 

 Himalaya, and both south-east Europe and the Rocky Mountains 

 severally possess a representative. Fossil forms are common in 

 the middle and upper Tertiaries of Europe, as far south as Sardinia. 

 Although the hare-tribe (Leporidcz) have an almost cosmopolitan 

 distribution, the majority of species of Lepus are inhabitants of the 

 Holarctic region, Central Asia being especially rich in representa- 

 tives of the genus. 



Among the Bovidtz, the bisons, which form a well-marked 

 group of the genus Bos, may be regarded as now characteristic of 

 the region, although the American Bos americanus ranges into the 

 Sonoran. In addition to the European B. bison, which was for- 

 merly spread over the greater part of Europe and during the 

 Plistocene extended into Arctic America, there is also the some- 

 what aberrant yak (B. grunniens) of Tibet, In the Plistocene the 

 range of the group was somewhat more extensive, remains of an 

 extinct species having been found in deposits of that age in 

 Texas ; and there is likewise another from the Pliocene of northern 

 India. The sheep constitute a group mainly characteristic of the 

 Holarctic region ; their headquarters being the Central Asian 

 plateau, where they are more numerous than anywhere else in 

 the world, although one species (Ovis vignei) impinges on the 



