THE BLACK WATER RAT 483 
Melanism (considered apart from the regular sub-species, A. a. vefa) 
is rather frequent, but local, being considered rare in the south of 
England and Wales. Millais gives a list of counties in which it has 
been observed, and remarks that the southern melanistic specimens 
are darker in summer than in winter, and are never so black as those 
from the north of Scotland, z.2., as JZ. a. veta. White spots on breast, 
forehead, or tip of tail are frequent (see Service, Aum. Scott. Nat. H7st., 
1904, 66-67). 
Skull (adults) :—Condylo-basal length, 40 to 44:6; breadth: at 
zygomata, 23-6 to 26; at inter-orbital constriction, 4-2 to 5-4; at occiput, 
17-8 to 20-6; median occipital depth, 10-4 to 11-6; length: of nasals, 
10-2 to 12-2; of diastema, 13 to 15-6; of mandible, 24-8 to 29-8; of 
maxillary tooth-row, 9 to 11-4; of mandibular tooth-row, 9-4 to 11-4. 
THE BLACK WATER RAT. 
ARVICOLA AMPHIBIUS RETA, Miller. 
1832. ARVICOLA ATER, William MacGillivray, Mem. Wernerian Nat. Hist. Soc., 
vi.. 429 (published January); described from Aberdeen, Scotland ; preoccupied 
by Aypudeus terrestris, B. ater of Billberg, 1827=Arvicola terrestris. 
1835. ARVICOLA AMPHIBIA, var. 8. A. ATER, Leonard Jenyns, Manual of British 
Vertebrate Animals, 33. 
Igto, ARVICOLA AMPHIBIUS RETA, G. S. Miller, junr., Proc. Biol. Soc. Wash, 
xxiii, 19, 23rd March; a new name for the preoccupied Arvicola ater of 
MacGillivray ; Trouessart ; Miller (Catalogue). 
History :—The Black Water Rat was described by MacGillivray in 
1830, as distinct from “the brown kind,” and confined to Scotland. 
He compared it only with brown individuals existing with it, with the 
result that he was unable to find satisfactory differences other than of 
size and colour, and consequently relinquished his species. In 1835 and 
1841, Jenyns (Ann. and Mag Nat. Hest., June 1841, 268-9), and 1846 
(Observations in Natural History, 76), confirmed the differences in size, 
but noted a few exceptions, the largest he had ever examined having 
been black. He reported the occurrence of Black Water Rats sometimes 
known as “ Water Moles,” in the fens of Cambridgeshire. In Norfolk, 
Lubbock also noticed them, and drew attention to the “considerably ” 
larger size of the brown forms, their different habits and custom of 
never mating with the black, thus suggesting their distinctness. In 
1892, H. A. Macpherson and Aplin (Zoologist, 281-293), tracing the 
distribution of melanism in Water Rats, found that, although occurring 
sporadically in many widely separated districts of England, it is well 
established only in the fen country of Cambridgeshire and Norfolk. 
In Scotland it is very local south of the Trossachs in the west and the 
watershed of the Tay on the east coast; north of these districts black 
