Red-backed Voles of Japan — JAMESON 
597 
KEY to SPECIES OF Clethrionomys IN japan 
1. Molars developing long roots in adults; postorbital crests poorly developed or absent; second 
upper molar and third lower molar not encapsulated in adults: (subgenus Clethrionomys ) 
I . rutilus 
Molars rootless except in very old adults; postorbital crests well developed; second upper 
molar and third lower molar usually encapsulated in adults (subgenus Aschizomys ) 2 
2 . Third upper molar with three inner salient angles (Fig. 1); tail less than one-half the 
body length; on Hokkaido rufocanus bedfordiae 
Third upper molar with more than three inner salient angles or loops although some pro- 
jections may be irregular or rounded (Fig. 1); on Honshu... 3 
3. Salient angles of all cheek teeth rounded or irregular, and triangles often open (Fig. 1); 
auditory bullae relatively small; in low elevation evergreen broad leaved forests of ex- 
treme southern Honshu ..imaizumii 
Salient angles more or less pointed, and triangles usually closed; auditory bullae relatively 
large; in coniferous forests of the northern half of Honshu.. 4 
4. Rostrum relatively long; anterior palatine foramina arise from about level of anterior 
molar alveolae; upper molar tooth row more than 6.0 mm niigatae 
Rostrum shorter; anterior palatine foramina arise from a point distinctly anterior to the 
level of anterior molar alveolae; upper molar row less than 6.0 mm... andersoni 
Clethrionomys rufocanus bedfordiae (Thomas, 
1905) 
Evotomys bedfordiae Thomas, 1905, Ab- 
stracts, Proceedings, Zoological Society of 
London, no. 23. (Holotype from Shinshi- 
notsu, near Sapporo, Hokkaido.) 
This is the form of rufocanus which occurs 
on the northern island, Hokkaido. It is a large, 
richly colored species with a tail of moderate 
length. It is difficult to compare bedfordiae with 
the other named subspecies: the illustrations of 
rufocanus shanseius (of the adjacent mainland) 
in Hinton (1926) are made from specimens 
which perhaps are not rufocanus and may not 
even belong in Clethrionomys. Presumably the 
nearest relatives live on the island of Sakhalin 
and the adjacent mainland. Clethrionomys siko- 
tanensis (Tokuda, 1935) seems to be quite dis- 
tinct from, although allied to, rufocanus; siko- 
tanensis is known from the Southern Kuriles 
and may be more closely related to lemminus. 
The skull of bedfordiae resembles the illus- 
tration of C. r. rufocanus in Hinton (1926: 
fig. 80 ) ; the depicted specimen is from an un- 
specified locality. Hinton’s illustration of C. r. 
shanseius (1926: fig. 83) is from the type series 
of Caromys inez; shanseius (from China) 
should be closer to bedfordiae than is typical 
rufocanus (from Sweden), but there is little 
doubt that Hinton’s illustration of shanseius 
represents a form at least specifically distinct 
from rufocanus. The enamel pattern (Fig. 1) is 
typical of C. r. bedfordiae and the third upper 
molar is especially characteristic. In 22 adults 
examined, 2 have distinctly rooted molars; in 8, 
the pulp cavities are more or less closed off, in- 
dicating that roots would probably have formed 
later in life. The anterior palatine foramina are 
expanded anteriorly and quite narrow poste- 
riorly and resemble C. r. rufocanus in this re- 
spect. The tail is less than one-half the body 
length. 
C. rufocanus bedfordiae is the most abundant 
microtine mouse on Hokkaido and is almost 
always more common than C. rutilus. In the ab- 
sence of any competing species of Microtus 
( which does not occur on Hokkaido) , rufocanus 
is sometimes a common inhabitant of open 
meadows and is of considerable economic im- 
portance (Ota and Jameson, in press). 
