THE MUCK GRASS MOUSE 441 



THE MUCK GRASS MOUSE. 



MICROTUS AGRESTIS LUCH} Barrett-Hamilton and Hinton. 



1913. MlCROTUS AGRESTIS LUCH, G. E. H. Barrett-Hamilton and M. A. C. Hinton, 

 Ann. and Mag. Nat. Hist., October 1913,366; described from Muck, Scotland; 

 type specimen, No. 14.1.30.2 of British Museum collection. 



Bistribution and History : — This Grass Mouse is only known from 

 tliree specimens taken on the island of Muck by Montague (see footnote 

 on p. 422 supra). It was found in short heather on the edge of a cliff, 

 where it appeared to be scarce. Millais had previously suspected the 

 existence of Grass Mice on the island. 



Description : — It is a quite distinct form, differing from exsul in its 

 smaller size, in which it approaches hirtiis ; agreeing with niial in its 

 only slightly less dense and shaggy coat, and with neglectus in its skull 

 and teeth ; and being quite peculiar in its conspicuously buff under-side. 

 The colour of the back is similar to that of mial, but owing to the 

 long black hairs becoming fewer and shorter laterally, the flanks are 

 lighter than those of the Eigg form, their colour gradually passing into 

 the heavy buff wash which extends all over the ventral surface of the 

 body and tail. This buff under - side is, however, here and there 

 darkened to a small extent by the slaty bases of the hairs which show 

 through. 



The skull cannot be distinguished from that of small examples of 

 neglectus ; it differs quite strikingly from that of niial in its smaller 

 size, relatively greater zygomatic breadth, broader brain-case, and 

 longer basioccipital. 



The teeth of the three specimens examined are normal, 111^ having 

 no trace of a fourth inner angle. 



Dimensions in millimetres of, respectively, a fully adult male (type 

 of the sub-species), a male, and an adult female : — head and body, 

 110, 108, 105 ; tail, 33, 32, 33; hind foot, 18, 17-5, 18; ear, 11-5, 

 II, II. 



Skull (of the type) : — Condylo-basal length, 26 ; breadth, zygomatic, 

 15-5; inter-orbital, 3; mastoid, ii-S; occipital depth, 6-6; length of 

 nasals, 7-2; of diastema, 7-2 ; of maxillary tooth-row, 6-3 ; of mandible, 

 i6-8 ; of mandibular tooth-row, 6-i. 



Status:— This mouse must apparently be regarded as a dwarfed 

 insular development of M. a. neglectus, the form inhabiting the 

 neighbouring Scottish mainland. The occurrence of an animal with 

 such relationships on Muck is remarkable, because on the closely 

 adjacent Eigg, as on Skye, Mull, Jura, Islay, Gigha, and Arran, the 

 Grass Mice are either identical with exsul, or more nearly related to it 

 than to neglectus. It would seem from the above facts that Eigg and 



' Luck in Gaelic means " mouse." 

 VOL. II. 2 F 



