6i4 



MURID^— EPIMYS 



support of his argument, reviewed above, as to the origin of the black 

 pelage in E. r. rattus. 



This melanism was at first supposed to be confined to Ireland; 

 Barrett-Hamilton received reports of it from at least seventeen Irish 

 counties, and there can be little doubt that it occurs in all the 

 remainder. He notes that " its appearance is sporadic and irregular ; 

 in some years it is absent, in others abundant, in the same locality. 

 The young exhibit the melanism from the beginning, and litters may 

 consist solely of black individuals or of some of each colour ; thus 

 Pack Beresford sent me a brown female, whose family consisted 



of eight brown and two black 

 young. Specimens exhibiting 

 intermediate coloration are rare ; 

 I have examined a parti-coloured 

 black and brown one {Zoologist, 

 1888, 142)." 



This variation has now, how- 

 ever, been recorded from the 

 Outer Hebrides ; from many 

 English counties ; from Paris 

 (Milne-Edwardes, Ann. Soc. Nat., 

 1 87 1, XV., art. 7) ; and Biarritz (a 

 specimen from this last place 

 seen by Barrett-Hamilton). 



There can be little doubt 

 that it is of frequent occurrence, 

 but is confused with E. rattus 

 or Arvicola amphibius ; for in- 

 stance, when observed in the 

 Zoological Gardens of London 

 it has done duty for E. rattus 

 (see Millais, ii., 211; Pocock, in 

 lit., to Barrett - Hamilton). It 

 seems to be a western develop- 

 ment of the species, and to 

 afford a close parallel, assuming de I'lsle's view to be correct, to the 

 relations subsisting between E. r. rattus and the wild-coloured forms 

 of that species. 



The skull (Fig. 91) is strongly built and of relatively large size (the 

 condylo-basal length usually more than 45 mm.). Compared with 

 E. rattus, the brain-case is relatively narrower ; the parietal region is 

 much less conspicuously vaulted, and the rostrum is larger, especially 

 deeper and broader. The dorsal profile is flatter and more nearly 

 horizontal throughout. The masseter and temporal muscles are 



Fig. 91. — Skull and Mandible of Efimys 

 norvegicus (life size). Reproduced from 

 Miller's Catalogue of Mammals of Western 

 Europe, by the kind permission of the 

 Trustees of the British Museum. 



