Quest 1948 Perognathus arenarius 7 May 6 Bahia Concepcion 13 mi S.F. Mulege Baja California Six males and one female caught in live traps baited with bird seed last night. Traps were set in sandy area in back of shell beach and below lava rocks. Traps were set among large bushes. All males had enlarged testes and the female one embryo (see catalog #140 to 146 incl.). May 7 Same location. Two females and one male caught (#154,155,156) last night in live traps set among large bushes of "Mangle Dulce" mixed in with creosote, Oclla, Kalo Verde, Cardone, and Elephantaphrium. One female had two embryos of 6mm each, the other no embryos. The male had enlarged testes of 9mm. This species of Perognathus is the most insistent of the mice caught so far, each individual being extracted from the live traps only with great difficulty, and always accompanied by squealing, jumping and biting. June 7 Punta Gasparino, 10'ft, 23°16'N, 110°9'W Baja California 5♂ + 4♀ (#316-324 incl.) caught in sand dune area last night. Live traps (48) were set just south of camp among short dense shrubs growing on sea side of silty sand dunes. The females had no embryos. These mice seem larger and much more mild tempered than those caught at Bahia Concepcion.