_Measurements._--The measurements of two males, Nos. 100184, 100182, and average and extreme measurements of five females, are, respectively, as follows: Total length, 257, 267, 244 (230-251); length of tail, 130, 128, 122 (105-129); length of hind foot, 32, 31, 31 (30-33); length of ear from notch, 16, 17, 15.3 (13.0-19); weight in grams, 71.5, 65.1, 50.8 (44.8-61.8); greatest length of skull, 35.2, 34.9, 33.6 (32.7-34.2); zygomatic breadth, 17.7, 17.5, 16.5 (16.1-17.1); interorbital breadth, 8.4, 8.1, 7.8 (7.5-8.0); length of nasals, 15.1, 14.9, 14.0 (13.3-14.5); width of braincase, 15.9, 15.1, 15.0 (14.7-15.1); alveolar length of upper molariform tooth-row, 6.0, 6.0, 5.6 (5.5-5.9). The measurements were taken according to the method of Goldman (N. Amer. Fauna, 34:10, 1911). Each of the specimens of which measurements are given above is adult; the transverse enamel fold has been obliterated in M1, is represented by only an isolated lake in M2 (except in one female where all trace of the fold has worn away) and is present in M3. _Specimens examined._--Total, 16, all from Michoacan, Mexico, and unless otherwise indicated in the University of California Museum of Vertebrate Zooelogy, as follows: 3 mi. NW Patzcuaro, 6700 ft., 1; 2 mi. W Patzcuaro, 7700 ft., 5; 2 mi. W Patzcuaro, 6700 ft., 2; Patzcuaro, 1 (U. S. Nat. Mus.); 5 mi. S Patzcuaro, 7800 ft., 7. * * * * * For the loan of comparative materials we are grateful to Dr. Harold E. Anthony of the American Museum of Natural History, Mr. Stanley P. Young and Dr. Hartley H. T. Jackson of the Biological Surveys Collection in the United States National Museum, Dr. Charles P. Lyman of the Museum of Comparative Zooelogy, and for assistance with the field work to the John Simon Guggenheim Memorial Foundation and to Miss Annie M. Alexander. _Transmitted April 1, 1948._ 22-3338