Range.—Central Veracruz, coastal plains and eastern slopes of the plateau of Central México, see [Figure 10]. Zonal range: Upper Tropical Life-zone (Lowery and Dalquest, 1951:537), parts of the Veracruz and eastern Transverse Volcanic biotic provinces of Goldman and Moore (1945:349). Occurs from near sea level at Boca del Río, Veracruz, up to 5500 feet 3 km. SE Orizaba.
Diagnosis.—Size medium to large for the species; ground color of dorsum of paratypes near Olive Brown; darkest of specimens of this subspecies examined (from Potrero Viejo, Veracruz) between Prouts Brown and Mummy [Pg 613] Brown; distal two-thirds of guard hairs of dorsum black, proximal third dark gray to sooty; hairs of dorsum black-tipped having subterminal band of Ochraceous-Tawny; sides paler (less of dark brown) than dorsum; venter Deep Olive Buff to clay color, individual hairs pale olive buff at tips, dark gray basally; region of throat and chin sooty gray; ventralmost vibrissae white to base, other vibrissae black to base; ears dark brown, sparsely haired; forefeet and hind feet flesh-colored in palest specimens, sooty in darkest; tail pale brown, slightly paler below than above; presphenoid only slightly constricted towards midline; average and extreme external and cranial measurements of 10 adults from Cerro Gordo, Veracruz, are as follows: total length, 118.9 (112-127); length of tail vertebrae, 45.1 (42-50); length of body, 74.0 (69-78); length of hind foot, 16.0 (16); length of ear from notch, 12.8 (12-13); occipitonasal length, 19.5 (19.0-20.0); zygomatic breadth, 10.3 (10.0-10.8); postpalatal length, 7.1 (6.7-7.5); least interorbital breadth, 3.9 (3.7-4.0); length of incisive foramina, 4.4 (4.1-4.6); length of rostrum, 6.9 (6.5-7.2); breadth of braincase, 9.5 (9.2-9.7); depth of cranium, 7.1 (7.1-7.4); alveolar length of maxillary tooth-row, 3.3 (3.2-3.3); for photographs of skull, see [Plate 1a], and [Plate 3a].
Comparisons.—For comparisons with B. m. nigrescens, see account of that subspecies. From B. m. pallidus, B. m. brunneus differs in: dorsal, lateral, and facial coloration deeper reddish brown, more melanins present; venter darker; buff gray rather than whitish buff to gray as in paratypical series; vibrissae black rather than brownish to white; tail sooty, less flesh-colored; forefeet and hind feet averaging slightly grayer; most external and cranial dimensions averaging slightly larger; nasals less attenuated; presphenoid less hour-glass shaped, sides more nearly straight.
From B. m. infernatis, B. m. brunneus differs in: side of face and neck deep reddish-brown rather than yellowish-gray (the differences in dorsal colorations are greater between brunneus and infernatis than between brunneus and pallidus); venter darker buff-gray; tail brownish rather than flesh-colored; forefeet and hind feet average slightly grayer; most external dimensions averaging slightly larger; cranial dimensions nearly the same except length of incisive foramina, which is smaller; presphenoid differs in much the same way as from pallidus.
Remarks.—Specimens from Chichicaxtle, Puente Nacional, 3 km. W Boca del Río, 1 km. E. Mecayucan, and Río Blanco (20 km. WNW Piedras Negras), are all paler than the paratypical series and other specimens from within the assigned range of B. m. brunneus. All these specimens from the coastal plain average considerably paler than those from the front range and slopes of the mountains. Specimens from Puente Nacional are intermediate in color between paler, grayish brown, specimens from the coastal plains and the darker, brown, specimens from the mountains. When Allen and Chapman (1897:203) described brunneus, they did so on the basis of the darker brown mice from the higher altitudes. The name, brunneus, sensu stricto, could be restricted to those mice from the higher altitudes of central Veracruz. However, when the mice of intermediate color from Puente Nacional are considered, it seems best to include the material from the coastal plain with brunneus. Crania from the higher altitudes are slightly larger than, but not significantly different from, crania of specimens from the coastal plains. Specimens examined from the coastal plains resemble the darker series of B. m. pallidus to the west in central México. But there is no evidence of gene flow between the paler coastal specimens and B. m. pallidus to the west. In fact, these paler brown mice on the coastal plain grade in color into the darker brown mice from the mountains. The paler mice from the coast may be an incipient subspecies.
The type and paratypes seem to have faded somewhat since they were described by Allen and Chapman (loc. cit.) and by Osgood (1909:259). However, the color of the paratypes and other specimens herein assigned is the feature most useful for distinguishing brunneus from all other subspecies of B. musculus.
Specimens examined.—Total 187 all from Veracruz, Republic of México, and distributed as follows: type locality, 4400 ft., 16[1] (including the type), 6[2], 1[3]; Cerro Gordo, 1500 ft., 19; Teocelo [= Texolo], 4500 ft., 1; 2 mi. NW Plan del Río, 1000 ft., 14[4]; Plan del Río, 1000 ft., 2[5]; Carrizal, 4[2]; Chichicaxtle, 3[2]; Puente Nacional, 500 ft., 1[5], 2; Santa Maria, near Mirador, 1800 ft., 10[2]; Boca del Río, 10 ft., 1[5], 8; Córdoba [= Córdova], 14[1]; 4 km. WNW Fortín, 4; Río Atoyac, 8 km. NW Potrero, 1; 2 km. N. Paraje Nuevo, 1700 ft., 9; El Xuchil, 1 mi. W. Paraje Nuevo, 6[6]; Potrero Viejo, 1700 ft. 15; Cautlapán [= Ixtaczequitlán], 4000 ft., 16; Micayucan, 1; 3 km. SE Orizaba, 5500 ft., 3; Río Blanco, 20 km. WNW Piedras Negras, 400 ft, 7; 29 km. SE Córdoba, Presidio, 15[4]; 3 km. N Presidio, 1500 ft., 2; Presidio, 600 meters, 6[3].
Marginal records.—Veracruz: type locality; Chichicaxtle; Boca del Río, 10 ft.; Río Blanco, 20 km. WNW Piedras Negras, 400 ft; Presidio; 3 km. SE Orizaba, 5500 ft.
[1] American Museum of Natural History.