Red-backed Voles of Japan — JAMESON 
599 
Clethrionomys andersoni (Thomas, 1905) 
Evotomys andersoni Thomas, 1905, Abstracts, 
Proceedings, Zoological Society of London, 
no. 28. (Holotype, from Tsunagi, Iwate- 
ken, Honshu.) 
This form is sometimes considered to be a 
subspecies of rufocanus, to which it is closely 
related. C. andersoni is easily separable from C. 
rufocanus bedfordiae by the longer third upper 
molar, which has four inner salient angles. C. 
andersoni is close also to C. niigatae, which is 
sometimes considered to be the same. Examina- 
tion of specimens of the type series of both 
andersoni and niigatae indicated that the two 
are distinct and that adults can be identified by 
the above key. 
C. andersoni is an inhabitant of coniferous 
forests in northern Honshu, in Aomori-ken, Fu- 
kushima-ken, and Iwate-ken, according to Imai- 
zumi (I960: 134). 
Clethrionomys niigatae (Anderson, 1909) 
Craseomys niigatae Anderson, 1909, The An- 
nals and Magazine of Natural History, vol. 
4, ser. 8: 317. (Holotype from Akakura, 
Niigata-ken, Honshu. ) 
For a very long period C. niigatae had been 
considered to be a synonym of C. andersoni; 
but, after studying specimens from the type 
series of both species, I agree with Imaizumi 
( I960) that the two are distinct species. In the 
nine adults examined, one specimen has closed 
pulp cavities and incipient roots. This is in 
contrast to the specimens examined by Imai- 
zumi (1957 and I960); the series in the Na- 
tional Science Museum in Tokyo all possess 
rootless molars. C. niigatae lives in the higher 
elevations of central Honshu. In Nagano-ken, it 
is found at approximately 1900 m. and higher 
among boulders both in virgin forests of fir and 
spruce and in rather open tangles of wild rasp- 
berries and currants. 
Clethrionomys imaizumii, new species 
TYPE: Adult male, skin and skull. Collected 
13 Feb. 1959, Nachi Falls, 300 feet elevation, 
Wakayama-ken, Honshu, Japan; E. W. Jameson, 
Jr., no. 1083. 
RANGE: Probably in broadleaved forests at 
low elevations in extreme southern Wakayama- 
ken (Kii Peninsula). 
DIAGNOSIS: A rather large, brightly colored, 
long-tailed species of the subgenus Aschizomys. 
Dorsum Rood’s Brown; venter Sayal Brown; tail 
bicolor, thinly haired, as in rufocanus and an- 
dersoni (color from Ridgway, 1912). Skull with 
rather small auditory bullae. Molars with angles 
rounded. 
MEASUREMENTS ( in mm. ) : Holotype ( and 
paratype): Total length, 194 (184); tail, 67 
(61); hind foot, 22 (21). Skull: condylobasilar 
length, 29.1 (skull of paratype damaged); zyg- 
omatic breadth, 15.6 (15.1); interorbital 
breadth, 4.3 (4.4); lambdoidal breadth 12.5 
( — ); alveolar length of upper molar row, 6.9 
(6.3 ); diastema, 8.3 (7.7). 
This species is most nearly like C. niigatae, 
but differs strikingly in the color and dentition. 
The molars are rootless with open dentine 
spaces in the two adult males seen. The enamel 
pattern is quite different, however: the triangles 
are rounded and indistinct and frequently open 
(Fig. 1 ) . The auditory bullae are markedly 
smaller. 
This species inhabits the luxuriant hardwood 
forests of the southern part oFthe Kii Peninsula 
in Wakayama-ken, the southernmost part of 
Honshu. Specimens were first collected by Dr. 
R. Kano; and Dr. Yoshinori Imaizumi kindly 
directed me to collecting localities. 
These four forms of the subgenus Aschizomys 
are separable on external characters, and these 
features are substantiated by constant dental 
and other cranial morphology. The relative 
proportions of the tail and body lengths are 
rather different for rufocanus, on the one 
hand, and for andersoni, niigatae, and imaizu- 
mii on the other hand. C. niigatae and 
C. imaizumii are long tailed. In nine specimens 
of niigatae from the upper slopes of Yatsuga- 
take, the tail is from 58 to 66 mm. in actual 
length, and the tail length is from 51 to 62 
per cent of the body length. In a series of 22 
adults of C. rufocanus bedfordiae from various 
localities in Hokkaido, the tail is from 34 to 56 
mm., and the tail length is from 28 to 46 per 
cent of the body length. It is quite possible that 
large series of both species would show some 
