432 MURIDiE— AGRESTIS 



M. hirtus is sufficient to account for the present restriction of the older 

 agrestis to islands, mountains, and northern regions, where the com- 

 petition is only moderately severe. In addition, the larger and 

 extremely palatable forms of Microtiis probably find a difficulty, like 

 the lemmings, in escaping from their enemies in the absence of 

 moderately heavy snow. They thus survive only where carnivora 

 are scarce, or where the coarse herbage both feeds and protects 

 them. This coarse herbage has no attractions for the newer dominant 

 species, which prefer the richer diet more easily obtainable in warmer 

 or more cultivated districts. 



The British sub-species are as follows : — 



MACGILLIVRAY'S GRASS MOUSE. 



MICROTUS AGRESTIS MACGILLIVRAII, Barrett-Hamilton and Hinton. 



1913. MiCROTUS AGRESTIS MACGILLIVRAII, G. E. H. Barrett-Hamilton and M. A. C. 

 Hinton, Abstract Proc. Zool Soc, London, No. 119, 15th April, 18, and Proc. 

 Zool. Soc, London, 1913, 831 ; described from Islay, Scotland ; type specimen. 

 No. 14 1. 30.1 of British Museum collection. 



Distribution and History : — This Grass Mouse appears to be con- 

 fined to Islay, where the existence of a "vole" seems to have been first 

 reported by T. F. Gilmour, who sent one found dead on 30th July 1905 

 to the editors of the ^««. .Scc^^. Nat. Hist. (1905, 242). An immature 

 specimen from Kildalton, too young for determination, was submitted by 

 Kinnear to Miller {Ann. and Mag. Nat. Hist., February 1908, 201); and 

 three young found in a rick were forwarded to Thomas by Russell 

 {Zoologist, 1910, lis), who did not think the animal common. A series 

 of fourteen caught by Sheppard in the woods around Bridgend at once 

 showed the distinctness of this mouse, which might well be called a 

 species were it not that the sub-specific name indicates its relation- 

 ships. Sheppard visited the island twice, and reported after his first 

 visit that the animal was very scarce, as he was only successful in find- 

 ing two colonies — one in a small belt of hazel, known as Dale Bush, the 

 other in a walled graveyard about two miles south of Fort Ellen, on 

 the border of the district known as the Oa. On his second visit he 

 found grass mice, shrews, and field mice all using the same runs in 

 open ground overgrown with brambles, raspberries, and coarse grass. 



Description: — MacGillivray's Grass Mouse resembles the more 

 widely distributed M. a. exsul (next to be described) in size and general 

 proportions, but may be recognised at all seasons by its much thinner 

 coat (length of dorsal hairs reaching about 8 mm.) and duller coloration, 

 especially on the under -side. The skull also shows some peculiar 

 characters, as described below. 



Colour : — The upper side is rich " buff," of a slightly duller tint than 



