THE ST KILDA FIELD MOUSE 541 
normal coloration, for Mr Eagle Clarke has found (of. cz.), from a long 
series of specimens taken in the months of September and October, that 
in about two-thirds of the adults, “and many of the immature ones, 
the throat, chest, and abdomen are white, and only washed with brown 
along the narrow median ventral line. As a result the demarcation 
between the peppery reddish-brown upper-, and the pale under-surface 
is pronounced in most examples, and renders the species very similar 
o” A. sylvaticus. “ About one-third of the adults and the majority of the 
younger specimens have the under-surface more or less strongly washed 
with buff? The dark dorsal line is well developed. In young 
individuals the backs are greyer, the bellies more rufous than in adults 
(see Steele Elliott’s description of the type specimen, Zoologzst, 1895, 
426). In the skull the smooth and rounded brain-case is rather 
depressed; the post-molar length is not shortened as is usual in 
hebridensts, though the bullze are rather small; and the nasals are 
relatively long (see proportional measurements in the table at p. 538). 
The cheek-teeth are as in sy/vaticus. 





Dimensions :— 
Condylo- 
Headand | gail, | Hind foot.| Ear. basal 
Ye length. 
1. Male, immature (type of species, No. 
94.7.16.1 of British Museum peleaeicn) 81 85 | 25 = 24°5 
2 Male, Henry Evans 107 91 24°5 17 231 
8. Male, largest recorded by Ww. Eag le 
Clarke. 129 109 26°5 17°5 
4, Female, Henry Ev: ans 110 94 24 15 (?) 
5. Female, largest recorded by w. agle 
Clarke . 126 110 25'5 19°5 
6. Average—20 males (Eagle Clark) é 109°8 94 2671 17°5 
7. Average—22 females (Eagle Clark) : 112 107 24:9 17-2 




1 Cheek-teeth only slightly worn. 
Remarks ;—Specimens with head and body between 100 and 113 mm. 
are probably adolescent; full-grown (which in most Muride means 
“ senile”) specimens are those with the head and body near 120 mm. 
For cranial dimensions, see table at p. 538 above. 
Status :—A. /irtensis is a well-marked member of the sylvaticus 
group. The latter has been established in Britain since the late 
Pliocene (Forest Bed), a fact which goes far to support the view that 
this species is truly indigenous upon St Kilda. The characters of 
A, fuirtensis are probably to be regarded as the results of insular 
specialisation. For remarks upon the position of /zrtenszs within the 
sylvaticus group, see above under Genus. 
Habits:—Mr Eagle Clark says that this mouse is most abundant 
where coarse grass prevails, although it is to be found almost every- 
where, as in the crofted area, the neighbourhood of houses, on the faces 
of the cliffs, and on the sides and tops of the hills. It finds congenial 
retreats in the rough stone-built “cleits,” and in the walls surrounding 
WOL, IT. 2M 2 
