THE BLACK WATER RAT 483 



Melanism (considered apart from the regular sub-species, A. a. retd) 

 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, i.e., as M. a. reta. White spots on breast, 

 forehead, or tip of tail are frequent (see Service, Ann. Scott. Nat. Hist., 

 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, 

 I7'8 to 20-6; median occipital depth, 10-4 to ii-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 ii-4; of mandibular tooth-row, 9-4 to 11-4. 



THE BLACK WATER RAT. 



A RV I CO LA AMPHIBIUS RETA, Miller. 



1832. Arvicola ATER, William MacGillivray, Mem. Wernerian Nat. Hist. Soc, 

 vi., 429 (published January) ; described from Aberdeen, Scotland ; preoccupied 

 by Hypudaus ierrestris, §. ater of Billberg, \%2T= Arvicola ierresfris. 



1835. Arvicola amphibia, var. ^. A. ater, Leonard Jenyns, Manual of British 

 Vertebrate Animals, 33. 



1910. 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 

 1 841, Jenyns (^««. and Mag Nat. Hist., June 1841, 268-9), ^n*^ 1846 

 {Observations in Natural History, y6), 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 

 neyer mating with the black, thus suggesting their distinctness. In 

 1B92, 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 



