_Records of occurrence_ (in each state the localities are listed from north to south).--Sinaloa: 2-1/2 mi. N El Fuerte, 25 K. U.; Sinaloa (Osgood, N. Amer. Fauna, 18:55, September 20, 1900); 10 mi. NNW Los Mochis, 18 K. U. Sonora: 1 mi. E Buena Vista, on Rio Yaqui Reservoir, 1000 ft., 2 K. U.; Camoa, 7 (U. S. N. M.); Tesia (Burt, Miscl. Publ. Mus. Zool., Univ. Michigan, 39:46, February 15, 1938); Alamos, 7 (U. S. N. M.); 4-1/2 mi. SE Alamos, 1000 ft., 5 K. U.; Chinobampo (Burt, _loc. cit._); 3 mi. NNW Bacarachi [= Bacavachi], 2 K. U. ~Perognathus goldmani artus~ Osgood _Perognathus artus_ Osgood, N. Amer. Fauna, 18:55, September 20, 1900, type from Batopilas, Chihuahua. _Range._--See map 1. _Measurements._--Average of five adult topotypes (Osgood, _op. cit._:55, 63): total length, 191; tail vertebrae, 106; hind foot, 24.6; occipitonasal length, 25.4; mastoidal breadth, 12.4; greatest width of interparietal, 7.1. _Remarks._--Considerable individual variation has been noted in each of several populations of _Perognathus goldmani artus_. For example, in 14 adults from Culiacan, Sinaloa, the variation is 25.0 to 27.9 in occipitonasal length and in mastoidal breadth is 12.6 to 14.0. Ten specimens (83122-83131 Univ. Mich.) labeled as from Carimechi, Rio Mayo, Chi[huahua], were recorded by Burt and Hooper (Occas. Papers Mus. Zool., Univ. Michigan, 430:6, May 27, 1941) as from "near Carimechi." They identified the two largest (83130 and 83131) as _Perognathus goldmani_ and the others as _Perognathus artus_. These identifications were reasonable in the light of knowledge available in 1941, but in the light of information presently available from the now more abundant material it is clear that all 10 of the specimens are _P. g. artus_. Examination (by Hall) of the specimens reveals that the differences relied upon by Burt and Hooper to differentiate the two species are well within the range of individual variation. For example, the variation (5.3 to 5.6 mm.) in width of the supraoccipital is less than in each of some other series of specimens of equal age of _P. g. artus_ from other localities. Also, there is geographic variation in the mice here assigned to the subspecies _P. g. artus_; skulls are smaller in the northern part of the geographic range and become gradually larger toward the south. In five adults from the northern part (Batopilas 3, and 26 mi. NE Choix 2) the mean of 12.6 of the mastoidal breadth of the skull is significantly smaller than the corresponding mean of 13.3 in 21 adults from the southern part (32 mi. SSE Culiacan 14, and El Dorado 7). The pelage of individuals from one and a half miles southwest of Tocuina is notably dark both above and below; the venter is dusky rather than white. We suppose that the darker color is a response to a dark-colored substrate--lava and soils derived from dark lava.