438 MURID^— AGRESTIS 



THE EIGG GRASS MOUSE. 



MICROTUS AGRESTIS MIAL,^ Barrett-Hamilton and Hinton. 



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

 Ann. and Mag. Nat. Hist., October 1913, 364; described from Eigg, Scotland; 

 type specimen, No. 14. 1.30.3 of British Museum collection. 



Distribution and History : — This mouse is at present only known 

 from the island of Eigg, where it was first taken by Montague in March 

 and April, and by Anderson in June 191 3 (see footnote on p. 422 supra). 

 Millais had previously suspected the occurrence of Grass Mice on Eigg. 



Description -.^M. a. mini agrees generally in size and proportions 

 with M. a. exsul, but differs strikingly in pelage. The fur is longer and 

 rather coarser in texture, so that the animal has a shaggy instead of a 

 sleek appearance. This is due in great measure to the abundance 

 and length of the long dusky hairs, which tend to darken the rump 

 and flanks, leaving the general colour of the back very much as in 

 exsul. The under-sides and the posterior surfaces of the hind legs are 

 silvery in sharp contrast with the dark brown flanks ; rarely the under- 

 side shows faint traces of a median stripe of yellowish wash. 



The skull differs from that of exsul of equal age in having the 

 nasals and basioccipital relatively a little shorter, and the auditory 

 bullae slightly smaller. 



The teeth are as in exsul Amongst nineteen specimens, the fourth 

 inner angle of m^ was entirely absent in only one ; in three it was 

 represented merely by a microscopic vestige ; in eleven it was small 

 but quite distinct ; and in four it was large and of regular form. 



Dimensions in millimetres: — head and body (young to middle- 

 aged), 98 to 116; tail, 27 to 39; hind foot, 17 to 20; ear, 10 to 13. In 

 the type these items are respectively 113 — 36 — 20 — 12. 



Skull : — Condylo-basal length of type (middle-aged), 27-4 ; breadth : 

 zygomatic, 15-7; inter-orbital, 3-5 ; mastoid, ii-8; occipital depth, 63 ; 

 length of nasals, 7-2 ; of diastema, 7-8 ; of maxillary tooth-row, 64; of 

 mandible, 17-9; of mandibular tooth-row, 6-3. 



Status : — This mouse, as is shown most clearly by its dental and 

 cranial characters, has its nearest ally in M. a. exsul It may be 

 regarded as a peripheral and local development of the latter, which 

 has arisen probably as a result of segregation for a long time upon a 

 small island. 



Habits: — Montague found this mouse common amongst coarse 

 heather ; it is not strictly nocturnal. 



' Mial in Scotch Gaelic is the general word for beast. 



