600 
PACIFIC SCIENCE, Vol. XV, October 1961 
overlap in this character but the difference is 
nevertheless real and fairly constant. C. imaizu- 
mii is a long-tailed animal like niigatae. The 
general fascies of the enamel patterns of C . ru- 
focanus bedfordiae, C. niigatae , and C. under - 
soni are angular (Fig. 1), but under soni and 
niigatae are distinct in having four inner salient 
angles in the third upper molar, whereas rufoca- 
nus bedfordiae has three. The enamel pattern of 
imaizumii is quite different in having the angles 
rounded, and there is a tendency for the loops 
and triangles to remain open ( Fig. 1 ) . The four 
species differ also in the form of the anterior 
palatine foramina. The hind foot of rufocanus 
bedfordiae is more densely furred than that of 
niigatae , imaizumii , and andersoni , but ail spe- 
cies are alike in possessing six plantar tubercles 
between which there are tiny projections. 
Imaizumi (1957) intimated that niigatae 
might be genetically distinct from rufocanus 
bedfordiae because the molars are rarely rooted 
in bedfordiae and., seemed never to be rooted in 
niigatae. In one specimen of niigatae examined 
by me, the pulp cavities are closed and there are 
Incipient roots. Later (I960) Imaizumi placed 
niigatae and andersoni in Aschizomys and kept 
rufocanus in Clethrionomys ; but such an ar- 
rangement does not indicate the nearness of 
these three species. As will be pointed out later 
in this paper, andersoni and niigatae almost cer- 
tainly emigrated from Hokkaido from a stock 
close to rufocanus. Imaizumi’s suggestion, rea- 
sonable as it may seem, simply emphasizes the 
weakness of the presence or absence of molar 
roots as a generic character in this case. 
Clethrionomys rutilus mikado (Thomas, 1905) 
Evotomys mikado Thomas, 1905, Abstract, 
Proceedings, Zoological Society of London, 
no. 23, p. 19 . ( Holotype from Aoyama, 
Hokkaido. ) 
This bright red little vole is quite unlike any 
other species in Japan. The color, rounded en- 
amel pattern (Fig. 1), well-developed molar 
roots, and small size separate rutilus from rufo- 
canus, the only other vole in Hokkaido. The 
molar row is rather short, as in Eothenomys 
smithi and E. kageus, and the enamel patterns 
are similar, but the angles are less rounded. In 
C. rutilus there are four' pairs of mammae. One 
specimen was examined. 
C. rutilus mikado is a rather uncommon 
dweller of the forests of Hokkaido and is not 
known to occur elsewhere In Japan. 
GENUS Eothenomys Miller 
The other genus of red-backed voles in Japan 
is Eothenomys ; most of the species occur in 
China and one ( melanogaster , the type of the 
genus) is found also on Taiwan. These species 
are quite close to Clethrionomys in general and 
some of them are perhaps related to the species 
of the subgenus Aschizomys In particular. In 
Eothenomys the color Is highly variable, but 
some species are reddish and so resemble the 
species of Clethrionomys, with which they have 
been confused on more than one occasion. 
Eothenomys differs in possessing rootless molars 
and only two or three pairs of mammae. Even in 
the oldest specimens there is no closure of the 
pulp cavities. The skull of Eothenomys is light 
and delicate and tends to be rounded; and the 
palate terminates in a shelf, as in Clethrionomys. 
key TO species OF Eothenomys IN japan 
1. Mammae four kageus 
Mammae six smithi 
Eothenomys smithi (Thomas, 1905 ) 
Evotomys smithi Thomas, 1905, Annals and 
Magazine of Natural History, series 7, vol. 
15, p. 493. (Holotype from Kobe, Hon- 
shu.) 
In Japan, the species smithi was described 
from specimens from Kobe, on the island of 
Honshu; smithi is also a common species on 
Shikoku and Kyushu, and a shorter-tailed sub- 
species ( okiensis ) was described from the is- 
land of Dogo in the Oki Group. The species 
smithi was described by Thomas in 1905, who 
at that time placed it in Evotomys ( = Clethri- 
onomys); and, noting some differences from the 
morphology of most species of that genus, he 
erected the subgenus Ehaulomys. Thomas stated 
then that smithi showed characters of Evotomys , 
Eothenomys, and Anteliomys. Externally smithi 
is similar to species of Clethrionomys , except 
that there are two or three pairs of mammae 
