532 MURIDA—APODEMUS 
that of sy/vatzcus, having the brain-case smoothly rounded ; in hamz/tonz, 
however, the fore part of the brain-case is angular and distinctly ridged. 
In all forms it is distinguished from sy/vaticus by its shorter post-molar 
length and smaller bulla, and usually by its greater palatal length, 
longer diastema, and tooth-row. These differences will be appreciated 
best from an examination of the tables on pp. 518 and 538. 
The external and cranial dimensions are given in the tables at 
pp. 536-9. Further special characters are noted under the sub-species, 
which are as follows :— 
(1) A. hebridensis hebridensis, de Winton. 
For Synonymy, see under species. 
Distribution :—Lewis, Outer Hebrides. 
Description :—The typical Hebridean Field Mouse differs from A. s. 
sylvaticus in its larger size, stouter build, longer feet, shorter ears, and 
dull under side. In general size it, when old, about equals 4. f. wznzonz, 
but its ears are smaller than those of the much smaller sy/vatecus. A 
pectoral spot is present and usually rather longer than in sy/vaticus, but 
not forming a collar. In colour the back and flanks are about as in 
sylvaticus. The typical adults from Uig, western Lewis, collected in 
September, have the under-parts heavily washed with buff, and show no 
distinct line of demarcation; the tail is uniformly brownish-grey, and 
is shorter and thicker relatively than in sy/vaticus. Attention was 
called by de Winton (Barrett-Hamilton, Proc. Zool. Soc., London, 1900, 
404) to the possible occurrence of sexual differences in the pelage of 
this form; he noticed that “young males appear to lose the dull hues 
of immaturity of the upper side, and to don the reddish colour of 
maturity at an earlier age than do the females, so that young males and 
females of the same age are actually distinguishable by their colour 
alone.” Ina series of seven adults collected by Mr Anderson between 
5th and roth April 1913, at Garrynahine, Callernish, western Lewis, the 
four females are like the Uig specimens, but the males have feeble 
pectoral spots and but slight trace of an abdominal yellowish wash, 
while the line of demarcation is rather sharply indicated. The females 
from Tarbet, Harris, are also like the Uig specimens in colour; as will 
be seen from the table at p. 536, both these and the mice from Caller- 
nish are smaller than the typical series, though the relative size of the 
feet and ears is the same. 
The skull differs from that of sy/vaticus in its larger size, narrower 
zygomatic, inter-orbital and cranial widths; the bulla are smaller, the 
cheek-teeth and diastemata longer—characters which are expressed in 
the shorter post-molar and longer palatal regions. 
Local variation :—Apart from the reduction of size noted above in 
a 
