700 RODENTIA 



SJiulI. — The skull so exactly resembles tliat of Microtus son- 

 day ensis isandayensis as to require no detailed description. Even 

 in a very old individual (Kinnear No. 321) the zygoma shows no 

 indication of the central expansion characteristic of M. orcadensis. 



Teeth. — The anterior loop of the first lower molar is inter- 

 mediate in form between that of orcadensis and true sandayensis, 

 though apparently nearer the latter. The outer re-entrant angle 

 tends to be shallow, so that its depth is usually much less than 

 that of inner angle, but the degree of this flattening varies so 

 much that specimens cannot be identified by this character alone, 

 while in at least one specimen (No. 321 Kinnear) the conditions 

 are exactly as in M. orcadensis. 



Measurements. — External measurements of type (adult female) : 

 head and body, 108 ; tail, 33 ; hind foot, 17 ; ear from meatus, 12. 

 Adult male and female from the type locality : head and body, 

 115 and 108 ; tail, 42 and 38 ; hind foot, 18 and 17 ; ear from 

 meatus, 1 1 and 1 1 . For cranial measurements see Table, 

 p. 699. 



Specimens examined. — Seven, all from Westray Island, North Orkneys 

 (B.M. and Edinburgh). 



6. Westray Island, Orkneys. N. B. Kinnear (c & p). 8. 1. 2. 1. 



(Type of subspecies.) 



MICROTUS SARNIUS Miller. 



1909. Microtus sarnius Miller, Ann. and Tilag. Nat. Hist., 8th ser., iii 



p. 420, May, 1909. 



1910. Microtus sarnius Trouessart, Faune !Mamm. d'Europe, p. 178. 



Tyj)''' locality. — St. Martins, Guernsey, Channel Islands. 



Geofirapliical distribution. — Island of Guernsey. 



Diagnosis. — Size about as in 3licrotus orcadensis or slightly 

 less (hind foot about 18*5 mm., condylobasal length of skuil 

 about 28 ram.) ; skull narrower than that of orcadensis, its 

 appearance in old individuals essentially as in the larger races of 

 M. agrestis ; colour agrestis-\\\ie, the underparts sharply con- 

 trasted pale grey. 



Colour. — The colour in summer in practically identical with 

 that of Microtus agrestis agrestis, though perhaps in most specimens 

 somewhat less dark and I'eddish. Underparts a light grey 

 (about the grey No. 9 of Ridgway) strongly contrasted with 

 wood-brown of sides, the belly sometimes with a faint buffy 

 tinge, the slate-grey appearing irregularly at surface, especially 

 in abraded skins. 



Skull. — In fully adult skulls the size and general appearance 

 is essentially as in the large forms of Microtus agrestis, though 

 the interorbital region is both longer and wider, the brain-case 

 is more depressed posteriorly, and the interparietal is noticeably 

 more quadrate in form, its antero-posterior diameter distinctly 

 more than half transverse diameter, its lateral extremities 



