ORKNEY VOLE. 109 



Macgillivray's Grass Mouse (J/. agrestis macgillivraii), a 

 rich buff-coloured form with thin fur, restricted to I slay, where 

 it is rare. 



Hebridean Grass Mouse (M. agrestis exsul\ common on 

 several islands of the Hebrides. Distinguished from the Field 

 Vole by its much larger size and duller brown colour. 



Eigg Grass Mouse (M. agrestis mial) restricted to the island 

 of Eigg. Differs from M. a. exsul in its shaggy coat of 

 abundant long hairs. 



Highland Grass Mouse (M. agrestis neglectus) found on the 

 summits of the highest Scottish mountains. It is larger than 

 the Field Vole, with thicker fur and darker, browner upper side. 

 It differs from M. a. exsul in the simpler character of the 

 first molar tooth. 



Muck Grass Mouse (M. agrestis hick}, of which only three 

 specimens have been taken, all on the island of Muck. About 

 the same size as the Field Vole, it has a buff underside. 



Orkney Vole (Microtns orcadensis, Millais). 



So far back as 1805 the Rev. George Barry, in his " History 

 of the Orkney Islands," mentions a rodent that was known 

 locally as the Vole Mouse, which he believed to be the same as 

 the agrestis of Linnaeus. He says it " is very often found in 

 marshy grounds that are covered with moss and short heath, in 

 which it makes roads or tracks of about three inches in breadth, 

 and sometimes miles in length,, much worn by continual tread- 

 ing, and warped into a thousand different directions." 



Towards the end of last century Mr. J. G. Millais obtained 

 specimens, and on a critical examination found that they 

 differed from the known forms in several details of skull 

 structure and in the folds and angles of the teeth, sufficient in 

 his opinion to constitute a new species, which he called Microtus 

 orcadensis. It is larger than the Field Vole, with a longer and 

 slightly broader head. 



