JCSimpson, 1938. 66. 270+ ft., Rancho de Costa Rica, Rio Sonora, Sonora. May 1, 1938, continued. Mr. Bliven showed us where we could comfortably camp under a large mesquite tree in a corral near the well (with wind mill, gasoline pump, and brick-tank). Set out 50 mousetraps and 50 live traps in a wheat-field next to a corn-field and bordered by mesquite trees. Dr. Benson, Senor Delgadillo, Jose Maria Coronado, and I used the "Borell-method" to catch bats at night by stretching wires close to the surface of the water of the brick-tank ( ). We used only two wires in a V. I was skeptical of this small surface- coverage, but the two wires stopped three Mastiff bats, two Brown bats, and 8x Mexican Free-tailed bats. I had seen some pipistrels flying while putting out my traps, but we were too late with the wires. May 2, 1938. In the mouse-traps in the wheat-field caught sonoriensis (topotype) 1 Perognathus flavus (0>269), 7 Reithrodonomys sp. (0>270- 274; ♀ 275, 276), one Perognathus penicillatus (not saved), one emb. no ♂ 277, 2 amb. ♀ 278), and 2 Peromyscus eremicus (0>279, ♀280). In the live-traps 5 Perognathus flavus sonoruum, (Hopotype) and 3 Reithrodonomys sp. These mice saved in live-traps to be put up later. (cf. p.68). Put 5 of the bats taken last night at the