_Specimens examined._--Total 149, distributed as follows: GUATEMALA: 1 mi. S Rabinal, 3450 ft., 14; 1/2 mi. N, 1 mi. E Salama, 3200 ft., 10; Lake Atescatempa, 10[7]. HONDURAS: Cementario, Gracias, 1[8]; Monte Redondo, 1[8]; El Caliche, Cedros, 1[8]; _La Flor Archaga_, 2[8], 1[9]; Hatillo, 1[8]; _type locality_, 7[8], 6[7] (including the type), 3[9]; _El Zapote_, _Sabana Grande_, 4[8]; La Piedra de Jesus Sabana Grande, 76[8]; _Cerro de las Cuches Sabana Grande_, 5. _Marginal records._--GUATEMALA: 1/2 mi. N, 1 mi. E Salama, 3200 ft. HONDURAS: El Caliche, Cedros; Hatillo; La Piedra de Jesus Sabana Grande; Cementario. GUATEMALA: Lake Atescatempa; 1 mi. S Rabinal, 3450 ft. [7] United States National Museum (Biol. Surv. Collections). [8] American Museum of Natural History. [9] Univ. Michigan, Museum of Zoology. =Baiomys musculus handleyi= Packard _Baiomys musculus handleyi_ Packard, Univ. Kansas Publs., Mus. Nat. Hist., 9:399, December 19, 1958. _Baiomys musculus musculus_, Goodwin, Bull. Amer. Mus. Nat. Hist., 68(1):39-40, December 12, 1934 (part); Miller and Kellogg, Bull. U. S. Nat. Mus., 205:512, March 3, 1955 (part). _Baiomys musculus nigrescens_, Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part). _Type._--Adult female, skin and skull; No. 275604 U. S. Nat. Mus. (Biol. Surv. Coll.); Sacapulas, El Quiche, Guatemala; obtained on April 24, 1947, by Charles O. Handley, Jr., original number 991. _Range._--Known only from the type locality in the valley of the Rio Negro. Zonal range: Part of the Chimaltenangan Province of Smith (1949:235). _Diagnosis._--Size medium to large for the species; dorsum Wood Brown in some series to Buffy Brown; guard hairs of dorsum black-tipped, color of underhairs Avellaneous; hairs white to base in region of chin, throat, and median venter; in lateral region, hairs Neutral Gray at base; dorsal surfaces of forefeet and hind feet and ankles white; tail white below, brownish above; nasals truncate anteriorly; frontoparietal suture forming an obtuse angle with the suture separating the parietals; alveolar length of upper molar tooth-row and tail long. Average and extreme external and cranial measurements for nine adults from the type locality are as follows: Total length, 121.4 (115-128); length of tail vertebrae, 50.7 (49-54); length of body, 70.8 (66-77); length of hind foot, 15.3 (15-16); occipitonasal length, 19.6 (18.8-20.7); zygomatic breadth, 10.5 (10.2-11.0); postpalatal length, 6.9 (6.4-7.4); least interorbital breadth, 4.0 (3.9-4.0); length of incisive foramina, 4.2 (4.0-4.5); length of rostrum, 7.2 (7.0-7.7); breadth of braincase, 9.8 (9.7-10.2); depth of cranium, 7.1 (6.8-7.2); alveolar length of maxillary tooth-row, 3.5 (3.4-3.6); for photographs of skull, see Plate 1_c_, and Plate 3_c_.