Quast 1948 Perognathus operatus 2 May 4 Mulege 25° ft Baja California 5 ♀ caught in lava rocks above creek by Dr. Benson and Tevis last night. Specimens put up by the two and caught in Museum Specials baited with walnut. May 5 Bahia Concepcion, 13 mi S.E. Mulege, Baja California Two males and two females caught in rocks above sandy area in back of beach last night. The males had enlarged testes, 7 and 14 mm, but no embryos were found in the females. Growing in the sand below the rocks are Mesquite, Cudnie, Cholla, and Pitaya. Caught in same habitat were Peromyscus eremicus (2♀). May 7 Same Location. Two males and one female (#151, 152, 153) caught among large "Mangle Dulce" bushes growing in sandy area behind shell beach N.E. of camp. Other plants growing in area were Creosote, Cholla, Cardone, Elephantaphrium and Palo Verde. One male had testes of 13 mm, the female had no embryos. May 8 Rancho Cadeji, S.W. end Bahia Concepcion, Baja California Two males (#157, 158) caught in live traps set on rocky hillside west of road. Only two animals were caught in 49 traps set. Sparse vegetation among the rocks - Barrel cactus, Elephantaphrium, Palo Verde, Creosote, and Cardone. Testes 15 and 11 mm. May 13 4 miles N. La Paz, Sea Level, Baja California One male (#182) caught in live traps set on