148 Mr. M. A. C. Hlnton o?i 



it is practically identical with Evotomys. But, living in the 

 high north, it has acquired the outward form of a lemming -, 

 and subsisting apparently upon a diet which rapidly wears 

 away the crowns of the cheek-teeth, the latter have become 

 hypsodont and rootless as in the higher voles. As in 

 Caryomys, the capsule of m' rises as a conspicuous hump 

 upon the floor of the orbit, while m.^ is strongly displaced 

 lingually by the shaft of the lower incisor. 



The Species and Subspecies o/Eothenorays. 



The known forms of Eothenomys may be referred, in my 

 opinion, to four species ; and they aflord an interesting 

 series of dental gradations. In each of the several forms 

 which are represented by fairly long series of specimens in 

 the material now before me, the enamel pattern of the 

 cheek-teeth appears to be very constant — and in this genus, 

 it would appear, therefore^ a fairly safe guide to the species 

 and subspecies. Of the species recognized in this paper, 

 E. melanoyaster and E.fidelis are dentally the most primi- 

 tive; in them m^ and m- (figs. 1-3) always possess a large 

 extra postero-internal angle (^' cusp 7t " ^)^ while ??i^ varies 

 considerably m complexity in different subspecies, although 

 its pattern seems to be tolerably constant in any given 

 form. 



E. fidelis, one of the new species described below, is dis- 

 tinguished from m el anog aster by its large size and by its 

 massive, narrow, and strongly ridged skull. It is apparently 

 confined to the Lichiang Range, where it is associated with 

 E. proditui\ a jiew species, which seems to constitute the 

 other extreme of the genus. E. melanoyaster is a widely dis- 

 tributed species, ranging from Southern Kansu eastwards to 

 "Western Fokien, and southwards and westwards, through 

 Sze-chwan and Yunnan^ into Assam and Burma. It is split 

 up into a considerable number of local subspecies, differing 

 from each other more or less in colour, in the complexity of 

 ??«', and in the relative sizes of the teeth and buihe, which 

 vary inversely Avith each other, large bullpe being correlated 

 with small molars and large molars with small bulia3. 



E. olitor, Thos., described from Chao-tung-fu, Yunnan, is 

 less primitive than fidelis and melanoyaster, since in it m^ 

 (fig. 4) has only three inner angles, having lost cusp n ; the 

 latter is, however, well developed in w^; wi^, on the other 



* For tliis nomeijclature of the cusps of Microtiue teeth, see Barrett 

 Hamilton and Hiuton. Hist. Brit. Maniiu. vol. ii. p. 504. pi. xxviii. 



