Relationships of the Red-backed Voles of Japan 
E. W. Jameson, Jr. 1 
Eastern Asia is particularly rich in genera and 
species of microtine rodents, some of which are 
more or less intermediate between Microtus on 
the one hand and Clethrionomys on the other. 
Where species of only these two genera are con- 
cerned, there is no problem of identity because 
there are differences in the color, in the struc- 
ture of the palate, and in the skull in general. 
The age of the specimen changes strikingly the 
condition of the cheek teeth, in which there are 
some of the most important generic features. 
Molars of immature specimens of Clethrion- 
omys , for example, are rootless, and resemble in 
this respect the molars of adult individuals of 
Microtus. In eastern Asia there are a number of 
species which resemble the species of Clethrion- 
omys in the palate, which terminates in a shelf, 
and are like Microtus s. str. in having rootless 
molars. For these forms which combine some of 
the structural characteristics of Clethrionomys 
and Microtus there are a number of generic 
names. A reviewer naturally wonders if his 
material contains mature individuals, and this 
doubt has caused some disagreement as to the 
proper generic allocation of red-backed voles 
of the Far East. 
The red-backed voles in Japan have been 
discussed by Hinton (1926), whose conclusions 
have been accepted by Eilerman (1941) and by 
Ellerman and Morrison-Scott (1951). Hinton 
(1926: 259-262) judged that several different 
forms were all based on immature specimens 
and placed bedfordiae, andersoni, and niigatae 
as synonyms of smithi . He very carefully ex- 
plained the pitfalls in separating voles on a small 
series and he emphasized the early age at which 
voles breed (and are apparently adult). In the 
Japanese forms in question, the age of the speci- 
mens is of great importance because these names 
were proposed for individuals in which the mo- 
1 Department of Zoology, University of California, 
Davis, California. Manuscript received February 10, 
1961 . 
lars are rootless, and Hinton’s conclusion was 
that they are all immature specimens. His cau- 
tion is certainly justified but can be carried to 
misleading extremes, for by combining several 
distinct forms as one, it is not difficult to show 
that a given character, in this case the condition 
of the molar roots, is indeed remarkably variable. 
There are remarks in Hinton’s appraisal of the 
situation that raise some doubts as to its appli- 
cation to the specimens he had at hand. For 
example, in reference to the small vole called 
smithi, he stated (1926: 260) that the type was 
a young male and added that . . by accident 
the fifty-three specimens of the series collected 
in Hondo, Kiushiu, and Shikoku, by M. P. An- 
derson in the following year are all young too.” 
It is possible, of course, to sample a population 
and obtain a series in which immature speci- 
mens predominate; but it is incredible that such 
an experienced collector as Anderson would 
have preserved 53 specimens of smithi from at 
least three widely separated localities and fail 
to include a single adult. Hinton added: 
Later on Mr. Anderson collected thirteen in 
Hokkaido. The majority of these are adult, some 
even old; in size, skull form, and tooth pattern 
they are strikingly different from the material 
referred by Thomas to E. — smithii. These were 
therefore described as a new species, E. ( Crase - 
omys) bedfordiae. But two specimens of this 
original series of E. bedfordiae are immature, 
and these are not distinguishable from the ma- 
terial upon which E. smithii was founded. 
These two presumably immature specimens 
could possibly belong to Clethrionomys rutilus, 
which is not uncommon in some parts of Hok- 
kaido; and, in this region, rutilus is a small 
bright short-tailed form somewhat like smithii. 
On the same page he dismissed the form de- 
scribed as E. ( C. ) andersoni with the comment, 
. . specimens, however, are merely large ado- 
lescents, intermediate in age between the adult 
material upon which E. bedfordiae was estab- 
lished and the immature material referred to 
594 
