Average measurements of 5 adult males of _R. m. zacatecae_ from the Pátzcuaro area showing much wear on the teeth compared with those of five specimens from the Zamora area, of corresponding sex and age of _R. m. saturatus_ reveal the smaller size of _R. m. zacatecae_. Total length, 157, 166; length of tail, 84, 84; length of hind foot, 19.6, 20.1; length of ear from notch in flesh, 14.8, 14.0; basilar length, 16.2, 16.6; length of nasals, 8.3, 8.5; zygomatic breadth, 11.1, 11.5; mastoid breadth, 9.9, 10.2; breadth of rostrum, 3.8, 4.0; interorbital construction, 3.2, 3.1; alveolar length of maxillary tooth-row, 3.5, 3.5; length of rostrum, 7.7, 8.0. =Reithrodontomys fulvescens tenuis= Allen Fulvous Harvest Mouse; Spanish, Ratón Moreno _Reithrodontomys tenuis_ Allen, Bull. Amer. Mus. Nat. Hist., 12:15, March 4, 1899, type from Rosario, Sinaloa. _Reithrodontomys fulvescens tenuis_, Howell, N. Amer. Fauna, 36:45, June 5, 1914. _Range._--Western part of state. _Specimens examined_, 27: nos. 100213-100216, 100274-100277, 100293-100311, distributed by localities as follows: 11 mi. W Zamora, 5,750 ft., 2; 6-1/2 mi. W Zamora, 5,950 ft., 2; 6 mi. W Zamora, 5,950 ft., 4; 1-1/2 mi. SSE Tacámbaro, 5,700 ft., 2; 1-3/4 mi. S Tacámbaro, 5,700 ft., 1; 1 mi. E and 2-1/2 mi. S Tacámbaro, 7; 4 mi. S and 1 mi. E Tacámbaro, 4,700 ft., 5; 1 mi. E and 5 mi. S Tacámbaro, 4,000 ft., 1; 1 mi. E and 6 mi. S Tacámbaro, 4,000 ft., 3. _Remarks._--Of the 19 specimens from the vicinity of Tacámbaro, only two have the underparts reddish as does _R. f. inexspectatus_. The upper parts are less reddish than in _R. f. inexspectatus_ but more reddish and less blackish than in _R. f. toltecus_ from the valley of México or than in _R. f. toltecus_ from Zamora. The external measurements and cranial measurements are less than in _R. f. toltecus_ or _R. f. inexspectatus_ and are as small as, or even smaller than, those of _R. f. tenuis_ to the northward or than those of _R. f. nelsoni_ to the westward. Relying only on printed descriptions of _R. f. tenuis_ and _R. f. nelsoni_, we are inclined to refer our specimens to _R. f. tenuis_ although the reddish color, we suppose, is evidence of intergradation with _R. f. nelsoni_ and _R. f. inexspectatus_. The four skins from Zamora are gray, as opposed to reddish, both above and below and in this respect they agree with the description of _R. f. tenuis_. They are lighter-colored (grayer) than either _R. f. toltecus_ or _R. f. inexspectatus_. The four specimens from Zamora are larger than animals from the vicinity of Tacámbaro and average slightly smaller than topotypes of _R. f. inexspectatus_.