Elliot (Field Columb. Mus., Zool. Ser., Publ. 79, 3(12):221, August 15, 1903) referred specimens from Rosarito and Rosarito Divide, San Pedro Martir Mts., Baja California, to _Perodipus_ [= _Dipodomys_] _agilis_. According to the currently known distribution of _Dipodomys agilis_ in Baja California (see Huey, Trans. San Diego Soc. Nat. Hist., 11:237, April 30, 1951), the specimens seemed likely to belong to the subspecies _D. a. martirensis_. An examination of the specimens (10644, 10690-10693 CMNH from Rosarito, and 10694 from Rosarito Divide) shows that, on the basis of large ear and comparatively narrow braincase, they are in fact referable to _D. a. martirensis_. Only No. 10693, with its broader braincase, seems atypical. Comparative materials used are in the Chicago Natural History Museum as follows: _D. a. martirensis_: Baja California: San Matias Spring, 2. _D. a. simulans_: Baja California: Ensenada, 8. California: Dulzura, 1 (topotype); San Luis del Rey, 3. ~Dipodomys agilis simulans~ (Merriam) J. A. Allen (Bull. Amer. Mus. Nat. Hist., 5:184, August 18, 1893) listed as _Perodipus agilis_ a specimen (6306/4941 AMNH) from Valladares, Baja California. Subspecies of this species were subsequently named without mentioning this specimen that, on geographic grounds, might be either _D. a. martirensis_ or _D. a. simulans_. Certain measurements of the specimen are as follows: Total length, 288; length of tail, 171; length of hind foot (dry), 41.0; greatest length of skull, 39.5; width of maxillary arch at middle, 4.5. The long tail and wide (4.5) maxillary arch are characteristic of _Dipodomys agilis simulans_ and constitute the basis for identifying the specimen as of that subspecies. ~Baiomys taylori analogus~ Osgood