MURIDZ—ARVICOLINA—EVOTOMYS. 135 
not all there are; and as a résumé 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 Arvicoline and 
Murine, 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 Synaptomys, Myodes, and 
Arvicola, having the external form of the first, the palate of the second, and 
the dentition (excluding its swz generis dental peculiarities) of the third. This 
is by no means an isolated ¢ase 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; 7. e., represents the inosculating point 
of its own with another group. It is through Evotomys, as a comprehensive 
type of Arvicoline, that Murine are related to all Arvicoline. We may sur- 
mise that Hvotomys remains nearest an original type of Glires, from which 
both the Murine and Arvicoline of the present day have descended; and 
that, while Synaptomys, Myodes, and Arvicola 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. ‘‘ gapperi”. 
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 Arvicoline 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 Hypudaus rutilus of authors (= Mus 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”. 
