Massive limestone outcrops rim many of the canyons in the mountainous country of Coahuila, Mexico. Caves and fissures in these cliffs afford living places for bats, owls, woodrats and other animals. In the course of field studies of the mammals of this Mexican state, many such places have been investigated in the hopes of obtaining specimens. On July 6 and 7, 1952, three members of a University of Kansas field party, Albert A. Alcorn, Jack M. Mohler, and Peter S. Chrapliwy, searched a cave three miles northwest of the city of Cuatro Cienegas in central Coahuila. No bats were found but approximately one-half peck of owl pellets, most of which were partly disintegrated, were collected. No owls were seen in or near the cave, but, judging from the large size of the pellets, they pertained either to the great-horned owl (Bubo virginianus) or to the barn owl (Tyto alba). This cave is situated approximately 100 feet up the west side of a narrow canyon above the road from Cuatro Cienegas northwestward towards Ocampo. A small stream fed by springs in the canyon flows southeastward through Cuatro Cienegas and the intermontane basin surrounding it and eventually leads into the Rio Salado. To the north and northwest the canyon leads on to a higher and more extensive desert basin which extends northward to the Texas Big Bend. The area surrounding Cuatro Ciengas has been well described by Gilmore (Jour. Mammalogy, 28:147-152, May 19, 1947), who reported on mammals taken there from archeologic cave-sites. The cave in question here is not one from which his archeologic materials were obtained. In all, 195 specimens were preserved well enough for accurate identification; this was done principally by the study of entire or partial crania. These specimens belong to 14 species which are listed as follows along with the number of each species present: Notiosorex crawfordi, 2; Antrozous pallidus, 6; Thomomys bottae, 1; Perognathus flavus; 42; Perognathus hispidus, 51; Perognathus nelsoni, 4; Perognathus penicillatus, 31; Dipodomys merriami, 22; Reithrodontomys fulvescens, 2; Onychomys torridus, 1; Peromyscus eremicus, 3; Peromyscus maniculatus, 1; Sigmodon hispidus, 23; Neotoma micropus, 5.