No actual intergrade between _nigriauris_ and _xanthogenys_ has been seen, although the specimens from Los Banos, referred to _xanthogenys_, have large skulls as in _nigriauris_. Intergradation with _latirostra_ is shown by specimens, referred to _latirostra_, from the Los Angeles area. Also the one adult male from 5 miles southeast of Santa Margarita, San Luis Obispo County, is of small size and in this respect approaches _latirostra_. The range of _nigriauris_ is separated from that of _munda_ by San Francisco Bay, Carquinez Straits, and I suppose by the lower part of the San Joaquin River. On the basis of color of the inside of the pinna of the ear, the two subspecies are uniformly distinct. Intergradation is assumed to occur through the subspecies _xanthogenys_. None of the 26 adult and subadult specimens examined for evidences of infestation of the frontal sinuses by parasites shows malformation of the sinuses. _Specimens examined._--Total number, 103, arranged by counties from north to south. Unless otherwise indicated specimens are in the Museum of Vertebrate Zoölogy. =California.= _Contra Costa County_: Glen Frazer Station, 1; 2 mi. W Pinole, 1[13]; 1 mi. E Pinole, 1; Richmond, 1[13]; Lafayette, 1; 7 mi. E Clayton, 1; Moraga Valley, 1; Pinehurst, Redwood Canyon, 1; Concord, 1. _Alameda County_: Berkeley, 11; Oakland, 1; Piedmont, 1; Haywards, 2; near Haywards, 2; 10 mi. E Haywards, 1[91]; Redwood Canyon, 1; Calaveras Dam, 1. _San Francisco County_: San Francisco, 11 (5[8], 2[91], 1[60], 1[7]); Ocean View, 1[68]; Visitation Valley, 1. _San Mateo County_: Moss Beach, 1; Half Moon Bay, 1; Redwood City, 1[87]; Menlo Park, 9 (5[87], 2[68]); no locality more definite than county, 1[8]. _Santa Clara County_: 1/4 mi. N Milpitas, 1; 1/4 mi. S Milpitas, 1; Stanford University, 6 (4[68], 2[91]); Palo Alto, 11 (6[41], 2[60], 1[75], 1[87]). _Santa Cruz County_: 3 mi. E Santa Cruz, 1; 2-1/2 mi. E Santa Cruz, 1; Santa Cruz, 6 (2[91], 1[68], 1[4]). _Monterey County_: 1 mi. E mouth Salinas River, 10 ft., 1[37]; Pacific Grove, 1[8]; Monterey, 2 (1[7]); Carmel, 1[8]; Carmel Valley, 1[68]; Point Lobos, 1; Gonzales, 1. _San Luis Obispo County_: 5 mi. SE Santa Margarita, 1; Morro, 1[91]; 3-1/2 mi. S Oceano, 6. _Santa Barbara County_: Santa Maria, 1[87]; 5 mi. N Las Cruces, 1; 7 mi. W Gaviota, 1; Gaviota, 1. =Mustela frenata latirostra= Hall Long-tailed Weasel Plates 1, 22, 23, 24, 34, 35 and 36 _Mustela frenata latirostra_ Hall, Carnegie Instit. Washington Publ. 473:96, November 20, 1936. _Putorius xanthogenys_, Baird, Mamm. N. Amer., p. 176, 1858 (part); Stephens, California mammals, p. 246, 1906; Merriam, N. Amer. Fauna, 11:25, June 30, 1896 (part). _Putorius (Gale) brasilianus frenatus_, Coues, Fur-bearing animals, p. 142 (part).