THE FIELD MOUSE 509 



Vid. Med. Nat. For. KJob., 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, ibid., 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, ibid., 1848, 2010), may possibly refer to 

 this species, but as W. Evans {in lit.) points out, the " small animals are 

 more likely to have been ' voles ' of some sort." In the 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 Microtus. 



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 sylvaticus than to fridariensis. 



Distribution in time : — The A. sylvaticus 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 oi A. sylvaticus (Newton, Vert. Forest Bed, pi. 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. whitei, 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. whitei also. 



Like the older forms of Evotomys, the Microtus agreftis group and 

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