MICROTUS 697 



MiCKOTUS SANDAYENSIS SANDAYENSIS Millais. 



1905. Microtus orcadensis sandayensis Millais, Mamm. Great Brit, and 



Ireland, ii, p. 280. 

 1908. Microtus sandayensis ]\Iiller, Ann. and Mag. Nat. Hist., 8th ser., i 



p. 199, February, 1908. 

 1910. Microtus sandayensis Trouessart, Faune Mamm. d'Europe, p. 177. 



Tijpe locality. — Sanday Island, North Orkney Islands. 



GeograpMcal distribution. — At present known from Sanday 

 Island only. 



Diagnosis. — First lower molar with anterior outer re-entrant 

 angle obsolete, much less developed than anterior inner angle ; 

 upper parts greyish brown, much lighter than in M. orcadensis ; 

 underparts whitish grey a little washed with buffy. 



Colour. — General effect of upper parts a clear, light hair- 

 brown, the individual hairs slate-black at base, those of underfur 

 tipped with a pale buffy drab, the exact shade between the 

 cream-buff and ecru-drab of Ridgway, the longer hairs black but 

 producing almost no effect of " lining." Underparts light grey 

 with a faint buffy tinge. Feet essentially like underparts. Tail 

 not distinctly bicolor, greyish white throughout but rather 

 strongly darkened by a sprinkling of blackish hairs along median 

 dorsal surface. 



Skull. — The skull, as already pointed out, is readily distinguish- 

 able from that of M. orcadensis by its lower, more flattened brain- 

 case, a character equally apparent whether the skulls are viewed 

 from above or behind. Zygomata scarcely expanded at middle, 



Fig. 138. 



Microtus sandayensis (a) aud («') ; 

 ^f. orcadensis (6). Nat. size. 



their form in this respect resembling that of M. arvalis rather 

 than that of M. orcadensis. They are, however, as short and as 

 widely spreading as in the more nearly related species. Inter- 

 parietal as in M. orcadensis. Auditory bullae slightly smaller 

 than in orcadensis. 



