V.] RODENTS. 183 



it, the family is thus essentially an Eastern Arctogaeic one; and it 

 may be assumed that, as its living representatives are inhabitants of 

 hot climates, the extinct forms were unable to exist sufficiently far 

 north to permit them to cross by the bridge of land via Bering 

 Strait. 



Among the rodents, in addition to the two widely spread 

 families Myoxidcz and Spaladdce. confined to Eastern Arctogaea, 

 we find in the Muridce the sub-family of the gerbils (Gerbillina) 

 similarly restricted, their range including the whole of Eastern 

 Arctogaea with the exception of the Malagasy region. 



The subfamily Murtna, which includes the true rats and mice 

 (Afus) is likewise restricted to the Old World. These rodents 

 differ from the hamsters (Cricetus) and the New World white- 

 footed mice (Sitomys), which, with other forms, constitute the 

 sub-family Cricetince, by the molar teeth in the upper jaw having 

 their tubercles arranged in three longitudinal rows ; whereas in the 

 latter they form only a double series. Distributed over all the 

 regions of Eastern Arctogaea, with the exception of Madagascar, 

 this group is also represented in the Australian region. Of the 

 two extensively distributed families restricted to the area under 

 consideration, the first is that of the dormice (Myoxidce) whose range 

 includes the Eastern Holarctic and Ethiopian regions. Distin- 

 guished from all other rodents by the absence of a caecum or 

 blind appendage to the intestine, and further characterised by 

 the complicated infoldings of the enamel on the crowns of their 

 molar teeth, these beautiful little creatures now attain their 

 maximum development in Africa. In a fossil state they are first 

 known from the lower Oligocene of Europe, and are likewise 

 common in the Miocene. Another family which does not range 

 beyond the limits of Eastern Arctogaea is that of the Spalacida, 

 typically represented by the great mole-rat (Spalax typhlus] a 

 blind creature, ranging over south-eastern Europe, Persia, Meso- 

 potamia, Syria, and Egypt. The allied genus (Rhizomys), in which 

 the eyes, although minute, are not covered with skin, includes 

 several species, whose distributional area embraces the north of 

 India, Tibet, China, Burma, Malaysia, and Abyssinia ; but the 

 three remaining genera are restricted to the Ethiopian region. 

 The whole of the foregoing belong to the mouse-like, or Myo- 



