_Pipistrellus subflavus clarus_ was taken along the Rio San Diego and the Rio Sabinas, both tributaries of the Rio Grande, where park-like stands of pecan, cypress, willow and other trees bordered these streams. The species was not found at stock ponds or along stream courses in adjacent places where such trees were absent. Funds for financing field work were made available by the Kansas University Endowment Association and the National Science Foundation. _Measurements._--Measurements of the holotype and average and extreme measurements of 5 adult females from the type locality, including the holotype, are, respectively, as follows: Total length, 85, 88.0 (85-92); length of tail vertebrae, 43, 40.8 (36-45); length of hind foot, 9, 9.4 (8.5-11); height of ear from notch, 12, 12.6 (12-13); length of forearm, 33.8, 33.4 (32.9-33.8); length of tibia, 14.8, 14.6 (14.5-14.8); greatest length of skull, 13.3, 13.1 (12.7-13.3); condylobasal length, 12.6, 12.4 (12.1-12.6); breadth of braincase, 7.0, 6.8 (6.7-7.0); zygomatic breadth, 8.1, 8.0 (7.8-8.2); mastoid breadth, 7.1, 6.9 (6.5-7.1); length maxillary tooth-row, 4.5, 4.5 (4.4-4.6). _Specimens examined._--Those from Texas are in the collection of the United States National Museum, and those from Coahuila are in University of Kansas Museum of Natural History. Total, 21. TEXAS: Comstock, 1; Del Rio, 2. COAHUILA: 2 mi. W Jimenez, 850 ft., 15; 2 mi. S and 3 mi. E San Juan de Sabinas, 1160 ft., 3. _Transmitted August 23, 1954._