484 MURIDAE—ARVICOLA 
individuals occur almost as generally as the brown. Macpherson and 
Aplin regarded these black animals as merely varieties. In 1910 
Miller (of. cz¢.) confirmed MacGillivray’s original opinion, but on 
different grounds. He showed that the black colour of Scottish 
individuals, being a geographically limited character accompanied by 
smaller size, is of sub-specific value. The sub-species undoubtedly needs 
further investigation, especially in regard to the black colony inhabiting 
the fen country, which may be composed only of melanistic examples 
of true amphibzus. 
Distribution :—North of the watersheds of the Clyde and Tay, the 
Black Water Rat is generally present and abounds in suitable streams 
and lochs, apparently to the exclusion of A. a. amphibius. There are 
no records as to how far it goes up the hills. Some writers (eg. 
Lydekker) report it as absent from Argyll, but this is not the case. 
In the Forth district a colony has been known to exist near Colinsburgh, 
Fife, for many years (W. Evans). On the other hand, records of it 
from the Orkneys (Baikie and Heddle, addendum) are probably based 
on confusion with. W7zcrotus orcadensis ; those from Islay, Mull (E. A. 
Alston), and Skye (Macpherson and Aplin, of. céz.), on MW. agrestis. 
This sub-species must not be confounded with sporadic instances of 
melanism occurring in England. In Cambridgeshire and Norfolk, 
however, black individuals predominate so as almost to suggest that 
they represent an isolated colony of MW. a. reta. 
Description :—This Water Rat is on the average smaller than the 
typical sub-species. The hind foot usually reaches a length of not more 
than 30-32, and the condylo-basal length of the skull usually less than 
42mm. The colour is normally darker, and black often replaces brown 
on the upper surface ; melanistic specimens are frequent. 
Black and brown individuals may occur in the same litter (W. Evans, 
Ann. Scott. Nat. Hist., 1910, 53). 
Skull (Adult Male, British Museum, 5.5.12.1): — Condylo-basal 
length, 41-9; breadth: at zygomata, 24; at inter-orbital constriction, 
4:2; at occiput, 18-5; median occipital depth, 11-3; length: of nasals, 
12-2; of diastema, 13-5; of mandible, 27-9; maxillary tooth-row, 10-4; 
of mandibular tooth-row, 10:3. 
Status:—Judging by its distribution and analogy with other 
mammals, the Black is an older form than the Common Water Rat, 
by which it has been driven out from the lower parts of the country, 
except perhaps Cambridge and Norfolk. But it cannot be a very 
old member of our fauna, since it is absent from all the Scottish 
islands. A statement of Boyd Watt—that the black form was first 
recognised in the Clyde area in August 1842 at Ballantrae, Ayrshire 
(whence John Thompson Sinclaire sent it to Thompson, see Waz. H7sz., 
Ireland, iv., 1856, 13), but by John Colquhoun’s time it had become 

