THE FAIR ISLE FIELD MOUSE 543 
JSridariensis also. It is, therefore, useful to retain /fridardenszs as a full 
species, because by doing so we are enabled to indicate the relationship 
of these insular Field Mice in a convenient manner. 
As Kinnear pointed out, A. frzdariensis has branched off from A. sy/va- 
vicus in a different direction from that followed by the Hebridean species, 
hebridensis and hirtensis ; in the present species there. is no increase in 
the relative size of the foot, and the ventral surface shows no tendency 
to become buff, and so cause the obliteration of the line of demarcation. 
Description :—A. fridarienszs differs from A. sylvaticus externally 
in its larger size, darker coloration, shorter ears, and relatively smaller 
palmar and plantar pads. The skull is characterised by its exceptionally 
slender rostrum; in the mandible the coronoid processes are usually 
small. Further details will be found below under the sub-species. 
(1) Apodemus fridariensis fridartensis (Kinnear). 
1906, MUS SYLVATICUS FRIDARIENSIS, N. B, Kinnear, Ann. Scott. Nat. Hist., 
April 1906, 68 ; type a male in the Royal Scottish Museum, Edinburgh ; described 
from Fair Isle, Shetlands ; Trouessart. 
1912. APODEMUS FRIDARIENSIS, G. S. Miller, Catalogue of the Mammals of 
Western Europe, 825. 
1914. A(PODEMUS) F(RIDARIENSIS) FRIDARIENSIS, M. A. C, Hinton, Ann. and 
Mag. Nat. Hist., July 1914, 132. 
Distribution :—Fair Isle. 
Description :—The general colour of the upper parts is like that of 
A. sylvaticus, but the long black hairs of the back and flanks are more 
numerous and give the fur a looser and harsher texture; these hairs 
cause the back to be more conspicuously clouded with black, and 
impart to the flanks a much darker, richer, and more heavily lined 
appearance. The line of demarcation along each flank is very regular in 
its course and very clearly defined. The ventral surface is of a uniform 
dull bluish-white throughout ; it shows no trace of a buffy suffusion, and 
usually no trace of a pectoral spot ; the latter is occasionally represented 
by a few brownish hairs. The feet are whitish. The upper surface of 
the tail is dusky, in sharp contrast with its whitish lower surface. 
The skull is large, and has the brain-case relatively long and 
narrow ; the temporal ridges are occasionally (eg., B.M., 6.11.18.4) 
sharply defined in old age, although they never impart such an angular 
appearance as is seen in old skulls of A. flavicollzs. The rostrum is 
long and slender; the masseteric plates of the zygomata are relatively 
broad, and project further in advance of the upper zygomatic roots than 
they do in A. sy/vaticus. The coronoid processes of the mandible are 
very short and slender. The cheek-teeth are as in A. sylvaticus. 
For external dimensions, see table at p. 544; the cranial measure- 
ments are given above in the table at p. 538. 
