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, 191 3, 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 cumbrce, 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, Ann. 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 h. hebridensis ; colour much darker than in cumbrce, 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 h. hebridensis 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 bullae. 



Closely related forms: — The field mice of Jura (referred Proc. 

 Zool. Soc, London, 1913,836, to A. s. sylvaticus), 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 fossae, 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 h. hebridensis 

 than does maclean, 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 



