Ventral view of body of a pregnant female to show details of mastology. Note the five pairs of mammae characteristic of weasels, and the uneven arrangement of mammae of the two sides which is also common among weasels.] [Illustration: FIG. 25. Map showing geographic ranges of the subspecies of _Mustela erminea_ in the New World.] For rearing their young, ermines live in burrows. Bishop (1923), in Albany, New York, found a burrow occupied by four young and a pair of adults. The burrow had many galleries and contained a nest constructed of rat fur, fine grass and fragments of leaves. At Woods Lake, Fresno County, California, in early August, Ingles observed (1942) some young and at least one adult at their den which was in a burrow beneath a hollow tree. The ermines used the hollow root and the hollow tree as well as the burrow beneath. Seton (1929 (2):591) quotes S. Eldon Percival, of Barretts Rapids, Ontario, as finding the living quarters of an ermine in unthreshed grain stacked in a barn and says (_op. cit._:590) that John Burroughs dug out a nest, composed of leaves and the fur of mice and moles, two or three handfuls in bulk, from a cavity the size of a hat, arched over with a fine network of tree roots. Four instances in which the male as well as the female was present at a den containing young are cited by Hamilton (1933:328) and he gives some evidence, although not at all conclusive, that "adults customarily pair, or at least run together, at times other than the breeding season." No other writers remark on this matter. I doubt that adult ermines are associated in pairs for most of the year but such may be the case. =Mustela erminea arctica= (Merriam) Ermine Plates 2, 3, 4, 9, 10, 11 and 41 _Putorius arcticus_ Merriam, N. Amer. Fauna, 11:15, pl. 2, figs. 1, 1a, and pl. 5, figs. 6, 6a, June 30, 1896. _Putorius_ (_Gale_) _erminea_, Coues, Fur-bearing animals, p. 109, 1877 (part). _Putorius richardsonii_, Bangs, Proc. Biol. Soc. Washington, 10:16, pl. 1, figs. 3, 3a, pl. 2, figs. 3, 3a, and pl. 3, figs. 6, 6a, February 25, 1896 (part). _Putorius cicognanii alascensis_, Osgood, N. Amer. Fauna, 19:43, October 6, 1900. _Putorius kadiacensis_, Osgood, N. Amer. Fauna, 21:69, September 26, 1901. _Putorius audax_ Barrett-Hamilton, Ann. and Mag. Nat. Hist., 13(ser. 7):392, May, 1904, type from Discovery Bay, Ellesmere Island. _Putorius alascensis_, Heller, Univ. California Publ. Zoöl., 5:345, March 5, 1910. _Mustela arctica arctica_, Miller, U. S. Nat. Mus. Bull., 79:97, December 31, 1912; Dice, Journ. Mamm., 2:22, February 10, 1921. _Mustela arctica_, Hall, Univ. California Publ. Zoöl., 30:420, March 19, 1929. _Mustela erminea arctica_, Ognev, The mammals of U.S.S.R. and adjacent countries, 3:31, 1935; Hall, Proc. California Acad. Sci, 23:559, August 22, 1944; Hall, Journ. Mamm., 26:179, July 19, 1945.