DE WINTON'S FIELD MOUSE 549 



always distinct from, frequently in close proximity to those of sylvaticus. 

 De Winton {op. cit, 442) states that all the specimens (of both species) 

 of which he records the dimensions " were caught within an area of 

 thirty acres, but the species did not intermingle; yet there was no 

 natural boundary or observable difference in the soil on which they 

 were found." Dalgleish {in lit., 17th November 1910) found it common 

 in parts of Surrey, where it occurred with sylvaticus. L. E. Adams 

 {MS^ finds it at Reigate associated with sylvaticus and with mice 

 which he considers to be intermediate between the two forms. 



A. f. wintoniis not known from Scotland, Ireland, nor any of the 

 smaller islands. 



The differential distribution of wintoni and sylvaticus within the 

 British area offers a certain analogy with that of the Common and 

 Pygmy Shrews. The restricted distribution of wintoni, coupled with 

 the fact that field mice of this type are not known in Britain before the 

 late Pleistocene, suggests that it is a comparatively recent immigrant. 

 The facts are susceptible of a different explanation, however. The 

 existing English stock of sylvaticus is quite possibly no older, since it 

 may also have arrived here in late Pleistocene times (see p. 510 above) ; 

 the sylvaticus-V^Q forms from the Upper Pliocene and the earlier 

 Pleistocene are in all probability distinct. From such earlier and 

 distinct stocks certain of the insular species (e.g. A. Jiirtensis) may well 

 have descended. The wider range of the modern stock of sylvaticus 

 in Britain and Ireland may in this case be due merely to some inherent 

 advantage as a colonist possessed by the smaller over the larger species. 

 The fact that in Norway and Switzerland flavicollis is the mountain 

 form and sylvaticus is the lowland species lends some support to this 

 latter hypothesis. Further close anatomical and palasontological 

 research will probably throw light on this interesting question. 



Description: — A. f. wintoni usually possesses a well-defined and 

 complete ochraceous breast-band or collar " about 8 mm. broad, pass- 

 ing along the chest immediately in front of the fore legs, with a cross 

 or longitudinal stripe in the centre extending forward about 5 mm., 

 and back along the sternum about 10 mm., where it is entirely lost" 

 (de Winton, op. cit., 442). The fur would appear to be somewhat 

 thinner than in the continental form, and the dark bases of the hairs 

 usually impart a more marked slaty tinge to the white under-parts. 



Young: — The juvenal pelage is plumbeous, as in sylvaticus. De 

 Winton {pp. cit., 443) stated that some trace of the pectoral collar 

 could be seen in specimens in this pelage ; this is confirmed by Adams, 

 who finds that all young in the first pelage show a collar of a dark 

 shade across the grey chest. Compared with the first pelage of 

 sylvaticus, the juvenal coat of wintoni is much whiter ventrally (L. E. 

 Adams, MS). 



