Fur above dusky gray tinged with yellow; beneath paler: tail more than half the length of the body.
A. amphibia, Desm. Mammal, p. 280. A. aquatica, Flem. Brit. An. p. 23. Water Rat, Penn. Brit. Zool. vol. 1. p. 118. Shaw, Gen. Zool. vol. 11. p. 73. pi. 129.
Length of the head and body eight inches four lines; of the head one inch ten lines; of the ears five lines and a half; of the tail four inches nine lines.
Head thick and blunt; eyes small; ears short, scarcely projecting beyond the fur; incisors of a deep yellow colour, very strong, and measuring in the lower jaw half an inch in length: fore feet with four toes and the rudiment of a thumb; hind feet with five; these last connected for a little way at their base, but not regularly webbed: tail more than half as long as the body, covered with short scattered hairs. Fur very thick, grayish black above, or reddish brown with scattered black hairs; beneath iron gray.
Var. β. A. ater, Macgillivray in Wern. Mem. vol. vi. p. 429. Fur of a deep black colour above and below.
Frequents the banks of rivers and ditches, in which it burrows. Swims and dives readily. Feeds principally on roots and tender plants. Produces in June from six to eight young. The black variety is not uncommon in the fens of Cambridgeshire: it differs in no respect but that of colour.