oper, 1936 1 mi. W summit Mt. Diablo, 3000 ft., Contra Costa Co., Calif. Mar. 22, A short overnight trip was made to the above locality - the same as for Feb. 16, 1936. The purposes of the trip, as regards mammal studies, were twofold. First, a larger series of Dipodomys h. was desired. Second, it was desired to determine, if possible, if a particular area which had been trapped fairly extensively about a month ago had become "re-infected" with Peromyscus. On Feb. 16, an area on a south-west facing slope was trapped well. Numerous Peromyscus mani- culatus and fewer Microtus californicus and Reithrodonmys megalotis were removed at that time. Now, would the an equivalent number of the same species be obtained on Mar. 22, or would other "less-forward" species be obtained - since Peromyscus perhaps would not "fill up the traps". The degree of error, of course, would be large considering the time lapse, the relatively small number of traps out, and the non-uniform traps - live traps were used on Mar. 22. 20 "Benson" live traps placed in the above area yielded the following: 2 Peromyscus maniculatus, 2 Reithrodonmys, 2 Desognathus californicus, and 1 Microtus californicus.