THE HEBRIDEAN FIELD MOUSE 535 
orbital region narrower, the brain-case broader and deeper, and the 
nasals, diastemata, and incisive foramina a little shorter. 
Related forms :—Similarly rufous, but larger forms are known from 
the islands of Gigha and Tiree (Proc. Zool. Soc., London, 1913, 836, 
where they were referred to A. s. sylvaticus). The only specimen from 
Gigha, an old nursing female, has the back and flanks slightly darker 
and a much more clearly defined line of demarcation; the tail is 
relatively shorter. The specimens from Tiree are externally much 
larger, with considerably shorter tails and ears than in casmbre, which, 
however, they strongly resemble in colour and the small size of the 
skull; in the latter the palatal length is slightly increased. 
(4) A. hebridensis maclean, Hinton. 
1914. APODEMUS HEBRIDENSIS MACLEAN, Hinton, Amn. and Mag. Nat. Hist, 
July 1914, 129; described from Mull, Inner Hebrides ; type specimen, a male, 
No. 15.5.29.27 of British Museum collection. 
1913. APODEMUS SYLVATICUS SYLVATICUS, G. E. H. Barrett-Hamilton and M. A. C. 
Hinton, Proc. Zool. Soc., London, 1913, 836 (in part). 
Distribution :—The island of Mull, Inner Hebrides. 
Description :—Size, and proportions of feet, tail, and ears nearly as 
in 4. hebridenszs ; colour much darker than in cumbre, the back clouded 
by relatively numerous long black hairs; flanks rather light, becoming 
more pallid below ; ventral surface nearly clear silver, with at the most 
only a feeble trace of the pectoral spot; the line of demarcation is 
somewhat irregular, and not at all sharply defined. The skull 
approaches that of 4. hebridenszs in size, differing in its exceptionally 
Narrow zygomatic arches, slightly narrower inter-orbital region and 
brain-case, the latter a little more depressed, and smaller bullz. 
Closely related forms:—The field mice of Jura (referred Proc. 
Zool. Soc., London, 1913, 836, to A. s. sylvatécus), judging from three 
specimens collected in May, have shorter tails and are still darker than 
those of Mull. In them the back is heavily clouded with black and 
the flanks are dark; the under-parts are clear silver with a very slight 
trace of the pectoral spot; the line of demarcation is straight and 
sharply defined. The skull has wider zygomatic arches, broader and 
deeper brain-case, longer pterygoid fossze, shorter nasals and diastemata, 
and broader incisive foramina and masseteric plates ; in some of these 
cranial features the Jura mice make a nearer approach to /. hebridensis 
than does szaclean, although in coloration they depart further from the 
typical form. 
Specimens from Islay, collected in May and August (at first referred, 
loc. cit., to A. s. sylvaticus), are much like maclean in general appearance 
and colour; they are, however, slightly smaller, with smaller feet, 
relatively longer ears and tail. The skull is distinguished by its 
