614 MURIDAZ—EPIMYS 
support of his argument, reviewed above, as to the origin of the black 
pelage in E. ~. 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 (Zoologzst, 
1888, 142).” 
This variation has now, how- 
ever, been recorded from the 
Outer Hebrides; from many 
English counties; from Paris 
(Milne-Edwardes, dzu, Soc. Nat., 
1871, 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 EF. rattus 
or Arvicola amphibius; for in- 
stance, when observed in the 
Zoological Gardens of London 
Fic. 91.—SKULL AND MANDIBLE OF Zp:mys jit has done duty for &. vattus 
hee Ge ie ee (see Millais, ii, 211; Pocock, zm 
Europe, by the kind permission of the 42, to Barrett- Hamilton). It 
Trustees of the British Museum. seems to be a western develop- 
ment of the species, and to 
afford a close parallel, assuming de I'Isle’s view to be correct, to the 
relations subsisting between Z. 7. 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 

