THE FIELD MOUSE 509 
Vid. Med. Nat. For. K70b., 1868, 51; Brown, Proc. Zool. Soc., 1868, 343 ; 
Miller, Catalogue, 804). 
In Britain it is probably, with Sorex araneus, the commonest small 
British mammal, of practically universal distribution; both species are 
very common in owl’s pellets, their numbers being only approached in 
certain situations by the Grass Mouse, which (Coward and Oldham, 
Cheshire, 273), although preponderating in certain limited areas, is 
not nearly so widely distributed as the Shrew and Field Mouse. The 
Bank Mouse is numerous, but also cannot compete with these two 
(Pocock, Zoologist, 1897, 507; Grabham, zbzd., 571). Traces of “a colony 
of some small animals” on the top of Maam Soul, Inverness-shire, at a 
height of between 3000 and 4000 feet, noticed by the Rev. G. Gordon 
(Zoologist, 1844, 424; A. Hepburn, zézd., 1848, 2010), may possibly refer to 
this species, but as W. Evans (cz /z¢.) points out, the “small animals are 
more likely to have been‘ voles’ of some sort.” Inthe Edinburgh district, 
according to W. Evans, it is common from sea-level to a considerable 
elevation in woods, fields,and natural pastures, but is more numerous in the 
plains and warmer valleys than in the damp uplands beloved of Mzcrotus. 
It is of widespread though less common occurrence in Ireland, and 
inhabits the islands off the west coast such as Inishmore and Clare. It 
occurs on Man, Anglesey, Bardsey, Lundy, Skomer, Lambay, Scilly, 
Wight, and the Channel Islands: it is common on Skye and Bute, but 
on the latter island its differentiation from the typical form has 
proceeded so far that it is now given distinct sub-specific rank. Field 
Mice inhabit Orkney (Barry, ed. ii., 1808), and a form much like typical 
sylvaticus occurs on the mainland of Shetland. Ogilvie-Grant has 
recently caught specimens of a long-tailed, rather pallid form on 
Sanday, Orkney; these were taken among the rough grass by the sea. 
The precise status of the Sanday Field Mouse cannot be settled 
without further material, but, judging from the skull, it is more nearly 
related to sy/vaticus than to /ridariensis. 
Distribution in time :—The 4d. sy/vaticus group dates from the late 
Pliocene (Forest Bed of Norfolk) in Britain, and in the earlier part of 
the Pleistocene it is known from the High Terrace and the older 
deposits of the Middle Terrace of the Thames. These older fossils are 
for the most part very fragmentary, and they prove little more than that 
the teeth of the earliest British Field Mice were similar in size and form 
to those of A. sylvaticus (Newton, Vert. Forest Bed, pl. xiv., fig. 11, a). 
A maxilla from the High Terrace, at Greenhithe, Kent, shows that in 
the skull of the form of this horizon (A. whztez, Hinton, Ann. and Mag. 
Nat. Hist., June 1915, 580) the posterior ends of the incisive foramina 
and the maxillo-palatine suture were a little more forwardly placed than 
in existing races. The Forest Bed and Middle Terrace forms may 
eventually prove to belong to A. whzte7 also. 
Like the older forms of Evotomys, the Microtus agrestis group and 
VOL, II. 2K2 
