THE ORKNEY GRASS MOUSE 461 



approximated anteriorly than in 0. orcadensis ; the jugals slender; m-^ 

 with the fourth outer fold sometimes as deep as in 0. orcadensis, 

 sometimes obsolete, as in 0. sandayensis. For external and cranial 

 measurements, see tables at pp. 463-4. 



(5) M. orcadensis sandayensis, Millais. 



1905. MiCROTUS ORCADENSIS SANDAYENSIS, J. G. MiUais, Mammals of Great 

 Britain and Ireland, ii., 280 ; described from specimens procured by George Sim, 

 from Sanday, Orkneys ; type, an immature male. No. 5.11.22.3 of British Museum 

 collection ; Hinton, Ann. and Mag. Nat. Hist., November 1913, 460. 



1908. MiCROTUS SANDAYENSIS, G. S. Miller, Ann. and Mag. Nat. Hist., February, 

 199 ; Pycraft, British Museum Guide to British Vertebrates ; Trouessart. 



1912. MiCROTUS SANDAYENSIS SANDAYENSIS, G. S. Miller, Catalogue of the 

 Mammals of Western Europe, 697. 



Distritoution : — Sanday, Orkneys. 



Description: — In size this sub-species about equals 0. orcadensis, 

 from which it is readily distinguishable by its lighter colour. The 

 upper side is nearer "hair-brown" than "mummy-brown," the tips of 

 the underfur being between "cream-buff " and "ecru-drab." The tail 

 is greyish white, sprinkled with blackish hairs along the median 

 upper surface. 



The skull differs from that of 0. orcadensis in its more depressed 

 brain-case (median occipital depth equals 50-52 per cent, of greatest 

 width across lateral processes of supra-occipital); less reduced inter- 

 parietal and smaller supra-tympanic fossae ; more constricted inter- 

 orbltal region, in which the squamosals are separated merely by the 

 inter-orbital crest (average distance between them 0-7 mm.), their 

 post-orbital crests salient (with well-marked antero-external processes) ; 

 slender jugals ; relatively slightly longer nasals and diastema ; and 

 slightly shorter cheek-teeth. 



In the teeth, m.^ has the fourth outer fold obsolete (Fig. 73). 



For external and cranial measurements, see tables at pp. 462-4. 



The well-beaten runs and thoroughfares of the Orkney 

 Grass Mouse are often conspicuous for long distances in 

 heather or other vegetation in rough fields or hills ; they are 

 either exposed, or form tunnels where vegetation is dense. 

 Their diameter is from 2 to 2.25 inches, or a little more than 

 the extreme spread of the animal's whiskers,^ and they may be 

 found in either dry or wet ground, in the latter case sometimes 

 tunnelling through saturated sphagnum by pools of water. 



' J. G. Millais, Zoologist, 1904, 244, and Mammals of Great Britain and Ireland, 

 ii. ; Robert Godfrey, Ann. Scott. Nat. Hist., 1905, 195; see also N. B, Kinnear, 

 Joum. cit., 241 ; for other references see Synonymy. 



VOI,. II. 2 G 2 



