THE NORTHERN GRASS MOUSE 429 



This division of Linnaeus's agrestis into two forms has long 

 been known, as to de S^lys 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 agrestis group ranges right across northern Asia, at 

 least to North-western Mongolia (J/, a. mongol of Thomas) 

 and Dzungaria {M. 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. M. pennsylvanicus 

 (Ord) of the eastern United States is so closely allied to M. 

 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 (Linnaeus). 



1761. Mus AGRESTIS (species), Carolus Linnaeus, Fauna Suecica, ed. ii., 11, No. 30 ; 



described from Upsala, Sweden (from the Mus agrestis minor of Gesner). 

 1766. Mus GREGARIUS (species), Carolus Linnasus, Systema Natura, xii., 84 ; 



described from Germany and Sweden. 

 1857. Arvicola agrestis (a.), J. H. Blasius, Stiugethiere 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. n. 2 E 2 



