Specimens obtained from Ebano, Pujal, and Tamuin, representative of _B. t. taylori_, are much paler on the belly and on the ventral surface of the forefeet and hind feet than are specimens from Ciudad del Maiz, representative of _B. t. fuliginatus_. The tail in _B. t. taylori_ is nearly unicolored and less hairy than in the paratypical series of _fuliginatus_. Specimens from 4 km. NE Ciudad Valles are nearly intermediate in color of the belly, dorsum, forefeet and hind feet, and tail, between the palest mice from the coastal plain and the darker mice in the mountains of the northeastern part of the State (specimens from El Salto average paler, however, than the type and paratypes). These specimens seem to be intergrades between _B. t. taylori_ to the east on the coastal plain and _fuliginatus_ to the northwest in the mountains. It seems best to refer the mice from 4 km. N Ciudad Valles to _B. t. taylori_ on the basis of the average of external and cranial characters. Specimens from 6 mi. SW San Geronimo, Coahuila, also referred to _B. t. taylori_, resemble in color the mice from 4 km. N Ciudad Valles. When more specimens are obtained from the front range of the Sierra Madre Oriental, at lower altitudes, the manner in which these two subspecies intergrade with one another will be better understood. At present, populations from higher altitudes in the mountains seem to represent a dark subspecies; populations from the coastal plain represent a pale subspecies, and those from the lower slopes and high valleys seemingly are intergrades. _B. t. fuliginatus_ occurs in a somewhat limited strip of chernozem soil (or suelos negros of Tamayo, 1949: Carta de Suelos). The populations occurring at lower altitudes on the coastal plain are on generally paler soils. _Specimens examined._--Total 39, all from the Republic of Mexico, as follows: SAN LUIS POTOSI: El Salto, 24 Mus. Nat. Hist., Louisiana State Univ., 7 Amer. Mus. Nat. Hist.; type locality, 8 (including the type). _Marginal records._--See specimens examined. =Baiomys taylori paulus= (J. A. Allen) _Peromyscus paulus_, J. A. Allen, Bull. Amer. Mus. Nat. Hist., 19:598, November 12, 1903; Elliot, Field Columb. Mus. Publ., 105(6): 136, July 1, 1905.