From B. m. grisescens, B. m. handleyi differs in: slightly paler above and below, primarily as a result of lacking buff-colored hairs; forefeet and hind feet white, not flesh-colored with gray overtones; tail bicolored, not unicolored; anterior tips of nasals truncate rather than flaring; tail and upper molar tooth-row longer.
Remarks.—B. m. handleyi seems to be restricted to the valley of the Río Negro, in the region of Sacapulas, Guatemala. Stuart (1954:7) points out that the Río Negro drops down into a gorge at a place near Sacapulas and flows northward through a deep canyon for approximately 60 kilometers. The Río Negro, then, flows onto the lowlands of the Yucatán Peninsula. The habitat is xerophytic in the valley of the Río Negro near Sacapulas. Stuart (op. cit.:10) suggests that this xerophytic habitat may be continuous to a place to the north of Chixoy, Chiapas, where the vegetation then becomes more mesic. The mesic conditions to the north in Tabasco and Yucatán probably have restricted the movement of pygmy mice to the north. No specimens of this mouse are known from the Yucatán Peninsula or from the State of Tabasco, México. B. m. handleyi intergrades with B. m. grisescens to the south. Specimens from 1 mi. S Rabinal, and those from a second locality 1/2 mi. N and 1 mi. E Salama, Guatemala, are intermediate in color of pelage between handleyi and grisescens. Stuart (op. cit.:5) mentions the continuity of habitat and tributaries from the Salama Basin into the valley of the Río Negro. Absence of physiographic and biotic barriers in the corridor between these two basins probably allows for some gene flow between handleyi and grisescens, and results in populations intermediate in color. To the north and northwest of Sacapulas, the Sierra de los Cuchumatanes rises abruptly and separates the known geographic range of handleyi from that of nigrescens to the north, while to the west the cactus-mesquite habitat of handleyi gives way to the oak-pine timber that, so far as known, does not support Baiomys. The difference in elevation and flora seems to restrict gene flow between handleyi and the more northern nigrescens. The only evidence of integration between these two subspecies is provided by one specimen from Chanquejelve, Guatemala. That specimen is intermediate in color between the pale handleyi and blackish-brown nigrescens.
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 Río 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; Teotitlán, Oaxaca, Republic of México, obtained on February 24, 1947, by Helmuth O. Wagner, original number 2702.
Range.—Southeastern Puebla, in the basin drained by the Río Salado and Río 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.