Reithrodontomys Apr.9 Muddy Creek, 1000 ft., 1 mi. S Cucharas Canyon, Monterey Co., Calif. seems largely traceable to the manner in which traps were set out. Night before last, Dale outtook us and trap-setting became more or less a matter of pacing off and dropping down; whereas, last night, traps were set more carefully in runs. Apr.10 Johnson Ranch, 800 ft., Cucharas Canyon, Monterey Co., Calif. Twenty-nine were caught in a line of 120 Museum Special traps which were set in a stand of Artemisia californica and grass on the margin of a young grain field. Reithrodontomys here again seems the most abundant of the small mammals. We let 7 of the animals which had been caught by their tails run free. These traps are a bit large for harvest mice and a distressing large percentage of the little beasts are merely caught by their tails. Most surprising to us was one of the traps which we turned over to find two Reithros caught in it! We photographed it. None of the females had embryos.