428 MURID^— AGRESTIS 



inner fold (counting from behind) fails to meet the third outer ; 

 or the anterior loop is complicated by the development of one 

 or more additional salient angles and infolds on either side 

 anteriorly. 



The British species and sub-species are as given below. 

 They fall into two groups : — 



1. Agrestis group. 



(i) M. agrestis macgillivraii, of I slay. 



(2) M. agrestis exsul, of the Outer and Inner Hebrides. 



(3) M. agrestis inial, of Eigg. 



(4) M. agrestis neglectus, of the Scottish Highlands. 



(5) M. agrestis luck, of Muck. 



(6) M. hirtus hirtus, of Britain south of the Highlands. 



2. Orcadensis group. 



(7) M. orcadensis ronaldshaiensis, of South Ronaldshay. 



(8) M. orcadensis orcadensis, of Pomona. 



(9) M. orcadensis rousaiensis, of Rousay. 



(10) M. orcadensis westrcs, of Westray. 



(11) M. orcadensis sandayensis, of Sanday. 



Much new material has been received only since the publi- 

 cation of the earlier pages on Microtince, and therefore two 

 sub-species of agrestis — mial and luch — and two of orcadensis— 

 ronaldshaiensis and rousaiensis — could not be included in the 

 Key to the Muridce on pp. 377-381. 



Group AGRESTIS. 



Miller grades all the west European Grass Mice having an 

 extra prism in n^ as sub-species of agrestis. This method, 

 however, obscures their relationships, especially the fact that, 

 as in Evotomys, a newer, smaller form, M. hirtus, has replaced 

 an older, larger, M. agrestis, the latter now confined chiefly 

 to northern regions, and with isolated southern colonies on 

 mountains. These two forms are of entirely distinct origin, 

 and are here given specific rank, and each has sub-species. 

 Like Lepus timidus, Evotomys skomerensis, alstoni, and erica, 

 M. agrestis belongs to an older fauna ; M. hirtus to that of 

 Lepus {Eulagos) europcEus and Evotomys glareoius. 



