_Remarks._--Specimens from Coahuila assigned to _planifrons_ compare favorably with topotypes of this subspecies although they are slightly larger in cranial dimensions (see tables 1 and 2). This small subspecies is darker and slightly larger than _subnubilus_ but in other ways is most closely related to _subnubilus_. _Cratogeomys c. planifrons_ shows little relation to other adjacent subspecies, including _tamaulipensis_, _subsimus_ and _rubellus_, all of which are considerably larger and paler. _Cratogeomys castanops planifrons_ is found in both deep and shallow soils of the high, open valleys of the Sierra Madre Oriental; in Coahuila it was taken at elevations as low as 7200 feet and as high as 8700 feet. _Specimens examined._--Total, 50, from: 4 mi. S and 6 mi. E Saltillo, 7500 ft, 7; 7 mi. S and 4 mi. E Bella Union, 7200 ft., 14; _12 mi. W San Antonio de las Alazanas_, 16; _12 mi. S and 2 mi. E Arteaga, 7500 ft._, 11; 2 mi. E and 2 mi. N San Antonio de las Alazanas, 8700 ft, 2. _Transmitted August 23, 1954._ 25-5679 * * * * * Transcriber's Notes: Emphasis Notation: _text_ - italicized +text+ - bold ~text~ - small caps Possible Typos Corrected Aquanaval => Aguanaval