The darkest of the material assigned to _canutus_ is from Nayarit (for specific localities see specimens examined). According to Tamayo (1949:Carta de Suelos), color of soil changes from chestnut in northern Sinaloa to black in southern Sinaloa and northern Nayarit. There seems, therefore, to be a close correlation between color of pelage and color of soil in this area. In Nayarit, particularly in the central and southern parts, the mice are intermediate in color between the paler, grayer population to the north and the more brownish samples, representative of _allex_ to the south. The coastal vegetation changes from the arid tropical thorn forests of the north and central parts of Sinaloa to a savannah in Nayarit, thence to a tropical deciduous forest farther south (see Leopold, 1950:508). In size and color, specimens from 3 mi. SE Tepic and 2 mi. SW Rosa Morada are intermediate between the larger, grayer _canutus_ and the smaller, light-brownish _allex_. In size of cranium, these specimens are more nearly like _canutus_, and are referred to that subspecies. Mice from the western coastal plain are relatively homogeneous as regards size of body and skull, except that those from 13.5 mi. S Acaponeta, Nayarit, average somewhat larger. _B. t. canutus_, like _B. t. subater_, is predominantly a lowland or coastal subspecies. The pallor of the former, that lives on generally paler soils, presumably is of adaptive value. Pygmy mice are seemingly rare in the northern part of the range of this subspecies. J. Raymond Alcorn and Albert Alcorn were successful in collecting only two specimens from the type locality after three successive nights of trapping with 100 traps set each night. Only six specimens are known from Sonora. These were obtained in the irrigated regions of Ciudad, Obregon, and Navajoa. Charles Sibley obtained one specimen 10.6 mi. SE Ciudad Obregon in a "maguey field." I obtained one specimen 1 mi. NNW Navajoa in a sparse grassway, 20 feet wide, bordering an open sewer, which coursed northward into the Rio Mayo. Irrigated wheat fields bordered the grassway and ditch. _Specimens examined._--Total 70 all from the Republic of Mexico and distributed as follows: SONORA: [Ciudad] Obregon, 4[44]; 10.6 mi. SE [Ciudad] Obregon, 1[45]; 1 mi. NNW Navajoa, 1. SINALOA: type locality, 2 (including the type); Culiacan, 175 ft., 2[46]; Mazatlan, 1[48]; _15 mi. N Rosario, Chele_, 300 ft., 35[47]; Rosario, 3[46]; Escuinapa, 5[48]; _Railroad Station Escuinapa_, 43 ft., 2[45]. NAYARIT: Acaponeta, 4[46]; _13.5 mi. S Acaponeta Junction_, 6[49]; 2 mi. SW Rosa Morada, 2; _2 mi. WNW Tepic_, 3200 ft., 1; 3 mi. SE Tepic, 1. _Marginal records._--SONORA [Ciudad] Obregon. SINALOA: type locality; Escuinapa. NAYARIT: Acaponeta; 3 mi. SE Tepic. SINALOA: Mazatlan. [44] Coll. Univ. California, Los Angeles. [45] Univ. California, Mus. Vert. Zoology. [46] U. S. Nat. Museum (Biol. Surv. Coll.). [47] Univ. Michigan, Museum of Zoology.