_R[attus]. rattus alexandrinus_ Hinton, Jour. Bombay Nat. Hist. Soc., 26:63, December 20, 1918. _Type._--From Alexandria, Egypt. _Remarks._--This subspecies seems to be rare in Washington. My specimens are all from small, isolated islands in the San Juan group. All were taken in the vicinity of human habitations. _R. r. alexandrinus_ resembles _R. r. rattus_, differing only in brown color of upper parts. =Rattus norvegicus norvegicus= (Erxleben) Norway rat _[Mus] norvegicus_ Erxleben, Syst. Regni Anim., 1:381, 1777. _Rattus norvegicus_ Hollister, Proc. Biol. Soc. Washington, 29:126, June 6, 1916. _Type._--From Norway. _Description._--Larger, heavier-bodied and coarser-furred than the black rat or roof rat with shorter, heavier tail. The tail is less than 50 per cent of the total length. The color of the back is dull, reddish brown, the sides are paler and the underparts are dirty gray. _Remarks._--The Norway rat was absent from the Pacific Coast of the United States before 1851. It probably reached the coast slightly after that date. It is common about all large cities in Washington. In the western part of the state it lives along streams and marshes under feral conditions. =Mus musculus= Linnaeus, subsp? House mouse _[Mus] musculus_ Linnaeus, Syst. Nat., 1 (ed. 10):62, 1758. _Description._--Size small; tail about 50 per cent of total length, naked; ears small, about 12 mm. in height; upper incisors not grooved; color of upper parts reddish or grayish brown; underparts brown or gray. _Remarks._--The house mouse became established in North America soon after its settlement by Europeans. It is now common throughout the state of Washington, principally near human habitations, but often lives in the wild. Races of the house mouse have been dealt with by Schwartz and Schwartz (1943: 59-72), and by Nichols (1944: 82-89), but lack of adequate material prevents subspecific identification of house mice from Washington at this time. =Aplodontia rufa= (Rafinesque) Mountain beaver _Description._--The mountain beaver is a stout-bodied animal about 14 inches in length, with a tiny tail that is almost invisible externally. The head is large, wide and low with small eyes, small ears and long vibrissae. The legs are short and heavy, but the forefeet are small and handlike; the hind feet are large and powerful. The claws of both forefeet and hind feet are long and strong. The pelage is short, coarse and rough. The upper parts are dark reddish brown and the underparts are grayish brown. The feet are pink. [Illustration: FIG. 121. Mountain beaver (_Aplodontia rufa rufa_), Seattle, Washington, March 19, 1940. (Fish and Wildlife Service photo by Victor B. Scheffer, No. 919.)]