_Baiomys musculus musculus_, Hall and Villa-R., Univ. Kansas Publs., Mus. Nat. Hist., 1:460, December 27, 1949 (part); Hall and Villa-R., Anal. del Inst. Biol., 21:196, September 28, 1950 (part). _Baiomys taylori taylori_, Dalquest, Louisiana State Univ. Studies (Biol. Sci. Ser.), 1:155, December 28, 1953 (part); Hall and Kelson, The Mammals of North America, 2:660, March 31, 1959 (part). _Baiomys taylori allex_, Hall and Kelson, The Mammals of North America, 2:659, March 31, 1959 (part). _Baiomys musculus musculus_, Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part). _Type._--Adult male, skin and skull; No. 120261 U. S. Nat. Mus. (Biol. Surv. Coll.); Zamora, Michoacan, Republic of Mexico, obtained on January 15, 1903, by E. W. Nelson, and E. A. Goldman, original number 15764. _Range._--Central and eastern Jalisco south into Michoacan, east through Guanajuato, Queretaro, thence into Estado Mexico, and Distrito Federal, and west-central Veracruz, see Figure 11. Zonal range: approximately the Transverse Volcanic Biotic Province of Moore (1945:218) and of Goldman and Moore (1945:349). Occurs from 5000 feet, 7 mi. S Ocotlan, Jalisco, up to 8000 feet in Ixtapalapa, Distrito Federal. _Diagnosis._--Size large for the species; dorsum dark Sepia to near blackish medially in freshly taken specimens (Sepia fading to near Fuscous in prepared specimens); belly slaty-gray, hairs Deep Neutral Gray near tips and Dusky Neutral Gray at bases; hairs on back black-tipped with subterminal band of Ochraceous-Tawny (guard hairs blackish to base); hairs of throat and chin white-tipped, gray at bases; dorsal vibrissae black, ventral and anteriormost vibrissae white; hairs on face and sides black-tipped, and Ochraceous-Tawny at base; ears sparsely haired, individual hairs grayish, blackish, and ochraceous; tail sooty to blackish dorsally, lighter ventrally; forefeet and hind feet sooty brown on dorsal and ventral surface. Skull relatively broad interorbitally; zygoma broad and squared; cranium larger in all dimensions than in most other subspecies. Average and extreme measurements of 10 adults from 1 mi. S, 11 mi. W Zamora, 5400 ft., Michoacan, are: total length, 109.4 (102-121); length of body, 64.3 (58-72); length of tail, 44.9 (39-51); length of hind foot, 14.6 (14-15); occipitonasal length, 18.0 (17.5-18.6); zygomatic breadth, 9.4 (9.1-9.7); postpalatal length, 6.6 (6.2-7.2); least interorbital breadth, 3.5 (3.3-3.8); length of incisive foramina, 4.0 (3.8-4.2); length of rostrum, 6.2 (5.8-6.5); breadth of braincase, 8.7 (8.5-8.9); depth of cranium, 6.6 (6.3-6.9); alveolar length of maxillary tooth-row, 3.1 (3.0-3.3); for photographs of skull, see Plate 2_a_ and Plate 4_b_.