THE ORKNEY GRASS MOUSE 459 
and without any antero-external process; the inter-parietal is slightly 
more reduced, the supra-tympanic fosse being much more extensive 
laterally. The jugals and m, are as in o. orcadens?s. For dimensions 
and cranial measurements, see tables at pp. 462-3. 
(2) M. orcadensis orcadensis (Millais). 
1904. MICROTUS ORCADENSIS, J. G. Millais, “Zoologist, July, 244; described from 
Sandwick, Pomona, Orkneys ; type, an old male, No. 4.6.21.1 of British Museum 
collection ; also, Mammals of Great Britain and Ireland, 1905, ii., 278, pl. 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 Guzde fo 
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. 
= a = 
— m2 — 
— ™ — 

Fic. 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. o. 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 
