Most of the specimens examined are immature and adequate adult cranial material has not been seen. Two adults, one of each sex, from Los Banos have skulls of large size which agree with those of _nigriauris_. The same is true of one adult and one young female from 4 miles southwest of Turlock, which, unlike the animals from Los Banos, show a darkening of the head extending in reduced degree even to the inside of the ears, as in _nigriauris_. The slightly darker than average (for _xanthogenys_) color on the back may indicate intergradation with _nevadensis_. Intergradation with _M. f. nevadensis_ is shown by specimens, from the southern part of the Sierra Nevada, mentioned in the account of _nevadensis_. None of the skulls shows malformation of the frontal sinuses such as result from infestation by parasites. _Specimens examined._--Total number 30, arranged by counties from north to south. =California.= _Sacramento County_: Bank of Sacramento River, 1[7]; 5 mi. S Fair Oaks, 1[29]. _San Joaquin County_: 4 mi. W Stockton, 1[74]. _Merced County_: Tegner School, 4 mi. SW Turlock, 2; Los Banos, 4 (2[74], 1[91] 1[87]). _Fresno County_: Mendota, 1[74]; Biola, 1[30]; Clovis, 1[55]; Fresno, 5 (1[74], 1[91], 2[55], 1[1]); 5 mi. W Fresno, 1[14]; Selma, 3 (2[50], 1[104]); 4 mi. NW Sanger, 1[55]; 5 mi. S Selma, 1[62]. _Tulare County_: Monson, 1[74]; 1-1/2 mi. N Goshen, 1[74]; Milo, 1[91]; 2 mi. N Tipton, 1[74]; Poplar, 2[53]. No locality more definite than California, 1[4]. =Mustela frenata nigriauris= Hall Long-tailed Weasel Plates 22, 23, 24, 34, 35, 36 and 41 _Mustela frenata nigriauris_ Hall, Carnegie Instit. Washington Publ. 473:95, November 20, 1936. _Putorius xanthogenys_, Baird, Mamm. N. Amer., 1858, p. 176 (part). _Mustela xanthogenys_ Gray, Ann. and Mag. Nat. Hist., 14(ser. 4):375, 1874 (part?). _Putorius (Gale) brasiliensis frenatus_, Coues, Fur-bearing animals, p. 142, 1877 (part). _Putorius xanthogenys xanthogenys_, Grinnel, Proc. California Acad. Sciences, fourth series, 3:292, August 28, 1913. _Mustela xanthogenys xanthogenys_, Miller, U. S. Nat. Mus. Bull., 79:99, December 31, 1912; Grinnell, Univ. California Publ. Zoöl., 40:102, September 26, 1933. _Type._--Male, adult, skeleton and skin; no. 32820, Mus. Vert. Zoöl.; Half Moon Bay, San Mateo County, California; received at Museum of Vertebrate Zoölogy, May 4, 1922, through A. L. Hagedoorn, after having been in captivity a few days where death occurred owing to injuries received in trap; original no. 1590.