DE WINTON’S FIELD MOUSE 549 
always distinct from, frequently in close proximity to those of sy/vaticus. 
De Winton (of. ctz., 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 (zz “¢., 17th November 1910) found it common 
in parts of Surrey, where it occurred with sylvaticus. L. E. Adams 
(ATS.) finds it at Reigate associated with sy/vaticus and with mice 
which he considers to be intermediate between the two forms. 
A. f. wintont is not known from Scotland, Ireland, nor any of the 
smaller islands. 
The differential distribution of wz¢ton¢ and sylvaticus within the 
British area offers a certain analogy with that of the Common and 
Pygmy Shrews. The restricted distribution of wzztonz, 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 sy/vatzcus is quite possibly no older, since it 
may also have arrived here in late Pleistocene times (see p. 510 above) ; 
the sy/vaticus-like 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. Airtens’s) 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 /lavzcol/zs is the mountain 
form and sylvaticus is the lowland species lends some support to this 
latter hypothesis. Further close anatomical and paleontological 
research will probably throw light on this interesting question. 
Description :—A. f wzutont 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, of. 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 sy/vatécus. De 
Winton (of. 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 wzzfonz is much whiter ventrally (L. E. 
Adams, J7S.). 
