The subspecies closest, geographically, to _B. m. handleyi_ is _B. m. nigrescens_, from which _B. m. handleyi_ differs more in color than from any of the other named subspecies, except _B. m. pullus_. There is a close correlation of pallor of mice and the xeric Rio Negro Valley, and the darkness (melanistic color) of mice and the mesic mountains and valleys to the north. _Specimens examined._--Total 49, from GUATEMALA: type locality, including the type: 12 (U. S. Nat. Mus., Biol. Surv. Coll.), 37 (Amer. Mus. Nat. Hist.). =Baiomys musculus infernatis= Hooper _Baiomys musculus infernatis_ Hooper, Jour. Mamm., 33:96, February 18, 1952; Miller and Kellogg, Bull. U. S. Nat. Mus., 205:512, March 3, 1955; Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959. _Baiomys musculus musculus_, Hooper, Jour. Mamm., 28:50, February 15, 1947 (part). _Type._--Adult male, skin and skull; No. 91497 Univ. of Michigan, Museum of Zoology; Teotitlan, Oaxaca, Republic of Mexico, obtained on February 24, 1947, by Helmuth O. Wagner, original number 2702. _Range._--Southeastern Puebla, in the basin drained by the Rio Salado and Rio Quiotepec, into northern Oaxaca. Zonal range: Arid Tropical in a part of the Orizaba-Zempoaltepec Faunal District of the Transverse Volcanic Biotic Province of Moore (1945:218). Occurs from 3100 feet in Oaxaca up to 6000 feet in Puebla. _Diagnosis._--Size medium for the species; dorsum Drab, terminal parts of individual guard hairs black, Neutral Gray basally, distal parts of underfur Pinkish Buff, proximally Neutral Gray; sides same color as dorsum; hairs in region of throat and chin white to base; venter whitish to Neutral Gray with tinges of Pinkish Buff; dorsal parts of forefeet and hind feet whitish with flesh-colored undertones, ventral parts whitish to dusky-gray; tail bicolored, grayish-brown above, white below; tip of tail not bicolored, instead grayish-brown throughout; ears pale brown, sparsely haired; incisive foramina long, not constricted posteriorly. Average and extreme external measurements for 9 adults from the type locality are as follows: total length, 113.9 (106-122); length of tail vertebrae, 44.1 (41-48); length of body, 71.0 (65-79); length of hind foot, 14.8 (13-16); length of ear, 11.9 (11-12). Average and extreme cranial measurements of 7 adults from the type locality are as follows: Occipitonasal length, 20.1 (19.7-20.4); zygomatic breadth, 10.4 (10.2-10.6); postpalatal length, 7.3 (7.0-7.7); least interorbital breadth, 4.2 (4.0-4.4); length of incisive foramina, 4.8 (4.4-5.6); length of rostrum, 7.2 (6.6-7.5); breadth of braincase, 9.6 (9.5-9.8); depth of cranium, 7.4 (7.1-7.6); alveolar length of maxillary tooth-row, 3.3 (3.1-3.4); for photographs of skull, see Plate 1_d_, and Plate 3_d_.