602 GEOGRAPHICAL RACES OF THE COMMON FIELD voLE. [May 19, 
M. agrestis and ML. neglectus may be, there can hardly fail to exist, 
in countries on the boundary-line of their respective ranges, 
intermediates whose presence would render it impossible to regard 
the two as distinct species. No doubt this was the right course to 
take so long as there was only open to naturalists the binomial 
system of nomenclature. It seems to me, however, that there is 
here a good case for the use of the trinomial system, especially as 
it can be done without inventing any new name. 
The Voles constitute so difficult a genus that it is not surprising 
that the distinguishing characters laid down by even such good 
naturalists as Jenyus and De Selys-Longchamps are not very 
clear, especially as they appear to have been given partially with a 
view to distinguish IM. neglectus from the Continental species 
M. arvalis, which was at that time supposed to occur in Great 
Britain, or to be represented there by a supposed nearly allied 
species M. britannicus; while, to further add to the confusion of 
ideas, the differences between If. agrestis and M. arvalis were very 
imperfectly recognized, if at all. I think, however, that De Selys- 
Longchamps’s remarks show that he applied the name of neglectus 
to one of the forms to which this paper refers: hence, if it be 
considered desirable, as I submit it is, to distinguish these two 
distinct forms by different names, the British and Southern form 
should, I think, be distinguished as J. agrestis neglectus, Jenyns, 
while the name of M. agrestis (Linn.) should be restricted to the 
more Northern form. 
The following are the characters of the two forms or sub- 
species :— 
Microrus acrusris (Linn.). 
This is a large Vole reaching when adult a length (head and 
body) of 130 millimetres and upwards. It differs in coloration 
from the Southern form, the upperside wanting the reddish tinge 
of British specimens, and the underside being of a purer white 
colour, most British examples having the underside washed with 
yellow. The skulls of the Northern form are much larger and 
stronger than those of the Southern, and the postorbital and other 
crests are more prominent. The whole skull is very Lemming- 
like in appearance, being much flattened and having the zygomatic 
arch very deep. 
Mr. Bonhote informs me that the Norway Voles were very 
Lemming-like in appearance when alive and he found them in- 
- habiting the same burrows as Lemmings. 
MIcROTUS AGRESTIS NEGLECTUS, Jenyns. 
This is a smaller animal, not averaging more than about 110 
millims. when fully grown. It may be distinguished by the cha- 
racters given above, viz., the size, cranial characters, and coloration. 
There is usually a reddish tinge on the upper surface of the adults 
and a yellowish wash to the belly, especially in summer, which, 
when present, is very distinctive. 
