UXJRIDM— ARVICOLINCE— EVOTOMYS. 135 



not all there are ; and as a resume of this attempt to indicate fully the rela- 

 tive position of the genus among its congeners, we may say Evotomys is a 

 true Arvicoline, yet it stands near the boundary between Arvicolince and 

 Murines, and especially approaches Onychomys of the latter subfamily ; and 

 that, though thus a connecting link between the two subfamilies, nevertheless 

 it stands in its own subfamily intermediate between Synapto?nys, Myodes, and 

 Arvkola, having the external form of the first, the palate of the second, and 

 the dentition (excluding its sui generis dental peculiarities) of the third. This 

 is by no means an isolated case where a certain form is "synthetic", inso- 

 much as it combines the peculiarities of several forms of its own group, and 

 is thus central so far as its own group is concerned, and yet is "peripheral" 

 so far as another group is concerned ; i. e., represents the inosculating point 

 of its own with another group. It is through Evotomys, as a comprehensive 

 type of Arvicolince, that Murines are related to all Arvicolince. We may sur- 

 mise that Evotomys remains nearest an original type of Glires, from which 

 both the Murines and Arvicolince, of the present day have descended ; and 

 that, while Synaptomys, Myodes, and Arvkola have been successively differ- 

 entiated from Evotomys, still this stands nearest the forking where the murine 

 series branched off from the arvicoline. 



A minute description of the teeth of Evotomys will be found under 

 head of A. "gapperV. 



The species of this genus are few in number; but, in the absence of 

 authentic skulls of some European and Asiatic animals that have been referred 

 to it, we cannot undertake to say how many there be. The North American 

 animals may be recognized at a glance among other Arvicolince by their prom- 

 inent ears and tawny-red color, due to the mixture of orange in the ferruginous 

 or chestnut that is a common tint with the other species. We have had the 

 pleasure of introducing a species not hitherto known to inhabit North Amer- 

 ica; and in our further account we hope to prove our present belief, namely, 

 that Arvicola or Hypudceus rutilus of authors {zzMus rutilus, Pallas) is a 

 species of circumpolar distribution, which, south of a certain isothermal, has 

 become differentiated into varieties known in North America as" gapperi", 

 and in Europe as "rubidus" and "glareola". 



