British Forms of X]^o(\cvn\\^. 13 i 



the young specimens from Lewis and Skye noted above ; if 

 this be so, the quite surprising similarity which exists 

 between this young animal and the adult pelage of A. epi- 

 nielas may serve as a hint of the nature of the ancestor of 

 the sijh-aticits group. 



Apodemus hebridensis fiolagan *, subsp. n. 



Aporieinus si/Iraticus sylvaticus, Barrett-IIainiltou Sc Ilinton, P. Z. S. 

 1913, p. 835. 



Hab. The island of Arran, Inner Hebrides. 

 Material exaiuiiied and dimensions. Nine, collected by 

 Mr. R. W. Shcppard:— 



Tail, Hind font. 

 Head without without 

 & body, hairs. claws. Ear. C.-b. 1. 



Average of 9 .... 98-3 84-5 23o 145 (of 6) 23o3 



Maxiumm lOo 8G 23-o (24) 14 (lo) 24 



Type 105 83 24 lo 24 



In the paper above cited Barrett-Hamilton and I described 

 this as " a rather large redilish mouse, with a tendency 

 towards the large foot and short ear of hebridensis." The 

 careful examination of the skull which I have since made 

 leads me to refer it to hebridensis and not to sylvaticus. 

 The peculiar characters of this form entitle it to subspecitic 

 rank. In addition to the external characters raeution(d 

 above, it is noteworthy that in the eight specimens, including 

 the type, which were collected at Brodick, Arran, the ventral 

 surface has no trare of a pectoral spot and is silvery, though 

 occasionally darkened to some extent by the slaty bases of 

 the hairs ; the line of demarcation is sharp. In a female 

 (no. Gl) from the cliffs near King's Caves there is a bright 

 pectoral spot which is continued backwards as a median 

 yellowish wash. 



The skull, though a little smaller than in h. hebridensis, is 

 distinctly larger than in ,9. sylvaticus. The average relative 

 dimensions show that it differs from true hebridensis princi- 

 pally in the lengthening of the pterygoid region, the post- 

 molar length being longer and the bullae smaller ; the nasals 

 are a little wider, the palatal length rather longer, the 

 diastema shorter, with somewhat smaller incisive foramina ; 

 the masseteric plate is distinctly broader and the molar 

 series longer. The differences noted appear to be correlated 

 with the muscular needs of a rather more powerful dentition. 



* Fiolafjun is the name of this moii.«e in the local Gaelic of Arran 

 {Alston). 



9* 



