THE NORTHERN GRASS MOUSE 429 
This division of Linnzus’s agrest¢zs into two forms has long 
been known, as to de Sélys in 1841. Although its meaning 
was not recognised, it was discussed by Blasius in 1857, and 
by myself in 1896. The scanty material available, and the 
lack of knowledge of the synonymy, structure, and geological 
history of the various forms long militated against a satisfactory 
use of the facts. 
The agrestts group ranges right across northern Asia, at 
least to North-western Mongolia (JZ. a. mongol of Thomas) 
and Dzungaria (7. arcturus of Thomas). 
In America it is represented by several allied but distinct 
forms which occupy the whole continent in subarctic, boreal and 
transitional zones, from Alaska to Labrador and Newfoundland. 
The group is thus quite comparable to others of circum- 
polar distribution. As it avoids the extreme north, it has no 
species common to the Old and New Worlds. JZ. pennsylvanicus 
(Ord) of the eastern United States is so closely allied to J/. 
agrestis in skull and teeth, that it has been used as an argu- 
ment for a recent Atlantic land-bridge (Scharff) ; but it is quite 
distinct in colour in a group where all the forms are closely 
allied. 
THE NORTHERN GRASS MOUSE. 
MICROTUS AGRESTIS (Linneus). 
1761. MUS AGRESTIS (species), Carolus Linneus, Fauna Suecica, ed. ii., 11, No. 30; 
described from Upsala, Sweden (from the AZus agrestis minor of Gesner). 
1766. MUS GREGARIUS (species), Carolus Linnzeus, Systema Nature, xii., 84; 
described from Germany and Sweden. 
1857. ARVICOLA AGRESTIS (a.), J. H. Blasius, Sdaugethiere Deutschlands, 369 
(part). 
Markmus of the Norwegians; not known to the French or Germans. 
This abbreviated synonymy is that of the species agrestis, the 
technical name of which admits of no doubt; since the typical sub- 
species is not found in Britain, there is no need for detail, which may 
be found in Miller’s Catalogue. That of the five British sub-species is 
given at length under each. As in the case of other animals (e.g., bats, 
shrews, and hares), there was formerly some doubt as to the identity 
of agrestis, owing to the presence of a second species, arvalis, which, 
although abundant in many parts of Europe, is not known in 
Skandinavia. 
VOL. II. Ee 
