JESimpson, 1938. 3400±ft., Arroyo Santa Rosa, 28 mi. N. Cumpas, Sonora. May 28, 1938 Caught in mousetraps on the rocky hill one Perognathus goldmani (σ7452; very much eaten by ants), 2 Perognathus baileyi (♂453; ♀454), and 9 Peromyscus cremicus (1 juveniles and one ant-fodder plus: σ7455; ♀456; ♀457, 458). Cheek-pouch contents of pocket-mice saved. Broke camp and drove over the continuing (since Moctezuma) difficult (rocky; rough; very steep in places) roads 1.2 miles to Rancho Santa Rosa, 17.7 miles to Bacoachic, and 41.6 miles more to Cananea where we bought a few supplies and drove on toward Santa Cruz—sunset near and area promising 16.1 miles from Cananae; so made camp at: 4700±ft., La Sauceda, 15 mi. DNE. Cananae, Sonora. Set 16 rat-traps for kangaroo-rats in rolling grassland (over-grazed) between river-bed and sierras. Dozens of the rat mounds could be seen in this grass- land where there is very little to cut off view for miles—only occasional bush with few trees and tall grass near the wash. May 29, 1938. Caught in rat traps only 3 Dipodomys spect- abilis (one juvenile and ♀459, ♀460; the embryos of the ♀460 measured 60 mm; cheek-pouch contents saved. Here using Schuyler and wooden rat-traps at mound sites resulted in much poorer catch than at Santa Ana (May 14, 1938) where I caught in the