THE FAIR ISLE FIELD MOUSE 543 



fridariensis also. It is, therefore, useful to retain fridariensis 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. fridariensis has branched off from A.sylva- 

 itcus 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. fridariensis 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. 



(i) Apodemus fridariensis fridariensis (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 19 14, 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 {e.g., B.M., 6.1 1. 18.4) 

 sharply defined in old age, although they never impart such an angular 

 appearance as is seen in old skulls of A. flavicoUis. 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. sylvaticus. The coronoid processes of the mandible are 

 very short and slender. The cheek-teeth are as in ^. sylvaticus. 



For external dimensions, see table at p. 544 ; the cranial measure- 

 ments are given above in the table at p. 538. 



