THE ORKNEY GRASS MOUSE 



459 



and without any antero-external process ; the inter-parietal is slightly 

 more reduced, the supra-tympanic fossae being much more extensive 

 laterally. The jugals and m-^ are as in o. orcadensis. For dimensions 

 and cranial measurements, see tables at pp. 462-3. 



(2) M. orcadensis orcadensis (Millais). 



1904. MiCROTUS ORCADENSIS, J. G. MiUais, Zoologist, July, 244 ; described from 

 Sandwick, Pomona, Orkneys; type, an old male, No. 4.6.21. i of British Museum 

 collection ; also. Mammals of Great Britain and Ireland, 1905, ii., 278, pi. 47 ; 

 Eagle Clarke and Bradley, Ann. Scott. Nat. Hist, 1905, 1-8 ; Forsyth Major, 

 Ann. and Mag. Nat Hist, March 1905, 323 ; Pycraft, British Museum Guide to 

 British Vertebrates; Trouessart ; Miller {Catalogue). 



Distribution : — Pomona and possibly Shapinshay, Orkneys. 



Description : — In this sub-species the colour of the upper side is rich, 

 dark brown, near " clove brown," overlaid with '' ochraceous buff," and 

 passing without sensible line of demarcation into the clear, bright 

 ochraceous buff of the under-side, the latter slightly obscured, especially 

 on the chin and throat, by the dusky hair-bases showing through. 



W3 



Fig. 73. — Right Cheek-TeeTH of Microtus orcadensis orcadensis (A, upper ; B, lower) ; 

 (C), Right m-^ of M. 0. sandayensis (A, B, and C 9 times life size) ; (D), posterior palate of 

 M. 0. sandayensis (5 times life size). (Drawn by M. A. C. Hinton.) 



The upper surface of the tail is blackish ; the under surface, with the 

 feet, light grey, tinged with ochraceous buff. The tail may have the 

 tip white (Millais). The soft first coat of the young is duller than in 

 adults, and at first always lacks the rufous tints on the belly ; later, the 

 belly may become rufous before the back gains the adult pelage 

 (Kinnear). 



The skull when adult has the brain-case short and broad ; the 

 occiput not depressed (median depth equals 55-56 per cent, of greatest 



