THE MUCK GRASS MOUSE 441 
THE MUCK GRASS MOUSE. 
MICROTUS AGRESTIS LUCH}: Barrett-Hamilton and Hinton, 
1913. MICROTUS 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. 
Distribution and History :—This Grass Mouse is only known from 
three 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 evsz/ in its 
smaller size, in which it approaches /zrtus; agreeing with szza/ in its 
only slightly less dense and shaggy coat, and with eg/ectus 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 mza/, 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 mza/ in its smaller 
size, relatively greater zygomatic breadth, broader brain-case, and 
longer basioccipital. 
The teeth of the three specimens examined are normal, 7! 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, 
HO; 10S) 105; tail, 33, 32, 33; hind! foot, 18, 17-5; 18; ear, 11-5, 
inti, ane 
Skull (of the type) :—Condylo-basal length, 26 ; breadth, zygomatic, 
15-5; inter-orbital, 3; mastoid, 11-8; occipital depth, 6-6; length of 
nasals, 7-2; of diastema, 7-2; of maxillary tooth-row, 6-3; of mandible, 
16-8 ; of mandibular tooth-row, 6-1. 
Status:—This mouse must apparently be regarded as a dwarfed 
insular development of J/7. 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 exsw/, or more nearly related to it 
than to weglectus. It would seem from the above facts that Eigg and 
1 Luch in Gaelic means “ mouse.” 
VOL. II. Pa) 
