75 Simpson, 1938 28. 775± ft., Tinajas de los Papagos, Sierra del Pinacate, Sonora March 23, 1938, continued ne Papago tanks. Also set out 21 rat traps in boulders along the edge of the wash containing the tanks. March 24, 1938 Two Neotoma lepida bensoni (♀♂58,59: ♀♀6) along large rocks of walls of wash of the Papago tanks. Along same trapline with mouse traps Dr. Benson caught seven Perognathus intermedius and two P. baileyi. 1000± ft., 2 mi. ne Tinajas de los Papagos, Sierra del Pinacate, Sonora March 24, 1938, continued. Nine Perognathus intermedius (60-68; JES; one ♀ no emb) in the coarse sand (cinders) and creosote at base of Sykes' crater: Nothing in the 50 live traps set at same place. These pocket-mice taken among creosote (fields of it with only an occasional ohotillo). Dr. Benson helped me Climbed to the rim of Sykes crater from which the desert could be seen for miles to the sand dunes of the Gulf of California. The Gulf itself was from here only barely perceptibly, but the mountains of Lower California were plainly visible. The surrounding desert lava fields are level with the rocky hills and mountains arising abruptly from the desert floor (as cinder cones or erosional remnants [or both?]); no such thing as "foothills" here. From this elev- ation (1000± ft.+ 300± ft. to rim) the vegetation appears very sparse because of its foliage-less character except the large wash which runs thru Papago tanks where