Chapter 4

Fig. 10.Distribution ofBaiomys musculus. Known localities of occurrence are represented by circles and black dots; the former denote localities that are peripheral (marginal) for the subspecies concerned.1.B. m. brunneus2.B. m. grisescens3.B. m. handleyi4.B. m. infernatis5.B. m. musculus6.B. m. nigrescens7.B. m. pallidus8.B. m. pullusNatural HistoryHabitat and numbers.—In Veracruz, Dalquest obtained the southern pygmy mouse in stands of tall grass (Spartina?) in sandy loam soil bordering, and in, dense vegetation; Davis (1944:394) found the species living in dense stands of grasses and seemingly utilizing underground burrows. Near Chilpancingo, Guerrero, rocky situations seemed to be the preferred habitat. Davis (loc. cit.) believedthat the species has a wide tolerance to kinds of habitats. In Morelos, Davis and Russell (1954:75) found these mice to be abundant along rock fences separating cultivated fields, and in arid lowlands. In Colima, Hooper (1955b:13) obtained specimens from an open thorn forest in sparse grass and rocky hillside bounding a stream and in litter below shrubs on the floor of a nut-palm forest; in Michoacán, these mice were taken in cane grass, shrubs, and mesquite near an irrigation ditch. From Guatemala, Goodwin (1934:39, 40) records specimens from Sacapulas, a hot, dry, sandy area where cactus and sparse grasses are present, and from La Primavera, on the edges of pine-oak-alder forests. Felten (1958:137) has takenmusculusfrom bushy areas in El Salvadore. In 1955, I obtained the southern pygmy mouse 6 mi. SW Izucár de Matemores, Puebla, along a stream in heavy grass bordered by cypress, willow, fig, bamboo, and in rocky grazed area near sugar cane fields.The southern pygmy mouse seems to be locally abundant in certain parts of its geographic range, and in other parts, scarce. For example, Dalquest (in. litt.) recorded the pygmy mouse as common at a place 2 km. N Paraje Nuevo, 1700 feet, Veracruz, where, by means of 50 traps, he took 14 of these mice in one night. The species was scarcer, although the habitat seemed suitable, 3 km. N Presidio, 1500 feet, Veracruz, where he caught only two pygmy mice in several days of trapping. Six miles southwest of Izucár de Matemores, the pygmy mouse was the most common rodent. I have trapped for it in Oaxaca and Veracruz in habitats that seemed almost identical to those mentioned by Dalquest, and also that at Izucár de Matemores, Puebla, with almost no success. The reason for the seeming disparity in numbers at different localities having nearly the same kind of habitat is unknown to me and bears further investigation.Behavior.—Little is recorded concerning the behavior of this species. David and Russell (op. cit.:76) found that of small mammalsB. musculuswas the first to appear at night. I caught mice of this species by hand in the afternoon in Puebla. They seemed to be active from noon until dark. Albert Alcorn wrote in his field notes that specimens were taken near noon at a place 9 mi. NNW Estelí, Nicaragua. My impression is thatmusculusis diurnal to crepuscular.Enemies and food.—Owl pellets (thought to be those of a barn owl,Tyto alba) from within the geographic range ofB. musculus, from 6 mi. SW Izucár de Matemores, yielded mandibular tooth-rows belonging tomusculus. Presumably, most of the carnivorous mammalsand raptorial birds within the range of the southern pygmy mouse could be listed as enemies. Diurnal to crepuscular habits of this mouse may protect it from some of the nocturnal carnivorous mammals and raptorial birds.Food of the southern pygmy mouse includes nuts, bark, grass seeds, and leaves. Dalquest (MS) writes that bits of banana proved to be useful bait in trapping these mice in Veracruz.Reproduction.—Notations concerning lactation and embryos on specimen labels of females suggest that the southern pygmy mouse breeds in all months. I have records of pregnant or lactating females in every month, save January, April, May, and June. The average of 26 counts of embryos or young per litter is 2.92 (1-4).Baiomys musculus brunneus(J. A. Allen and Chapman)Peromyscus musculus brunneusJ. A. Allen and Chapman, Bull. Amer. Mus. Nat. Hist., 9:203, June 16, 1897; Elliott, Field Columb. Mus. Publ., 105(4):136, July 1, 1905; Elliott, Field Columb. Mus. Publ., 115(8):203, 1907; Osgood, N. Amer. Fauna, 28:259, April 17, 1909.Baiomys musculus brunneus, Miller, Bull. U. S. Nat. Mus., 79:137, December 31, 1912; Miller, Bull. U. S. Nat. Mus., 128:318, April 29, 1924; Ellerman, The Families and Genera of Living Rodents, 2:402, March 21, 1941; Goldman, Smith. Miscl. Coll., 115:437, July 31, 1951; Goodwin, Bull. Amer. Mus. Nat. Hist., 102:318, August 31, 1953; Miller and Kellogg, Bull. U. S. Nat. Mus., 205:512, March 3, 1955; Booth, Walla Walla Publs., Dept. Biol. Sci., 20:15, July 10, 1957; Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part).[Peromyscus musculus]brunneus, Elliott, Field Columb. Mus. Publ., 95(4): 176, 1904.Peromyscus musculus[musculus], Osgood, N. Amer. Fauna, 28:258, April 17, 1909 (part).Baiomys musculus musculus, Davis, Jour. Mamm., 25:394, December 12, 1944 (part); Goldman, Smith Miscl. Coll., 115:437, July 31, 1951; Hooper, Jour. Mamm., 33:97, February 18, 1952 (part); Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part).B.[aiomys]m.[usculus]brunneus, Hooper, Jour. Mamm., 33:96, February 18, 1952.Baiomys taylori, Hooper, Jour. Mamm., 33:97, February 18, 1952 (part).Type.—Adult female, skin and skull; No. 12535/10845 American Museum of Natural History; Jalapa, Veracruz, Republic of México; obtained on April 13, 1897, by F. M. Chapman, original number 1203.Range.—Central Veracruz, coastal plains and eastern slopes of the plateau of Central México, seeFigure 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, seePlate 1a, andPlate 3a.Comparisons.—For comparisons withB. m. nigrescens, see account of that subspecies. FromB. m. pallidus,B. m. brunneusdiffers 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.FromB. m. infernatis,B. m. brunneusdiffers in: side of face and neck deep reddish-brown rather than yellowish-gray (the differences in dorsal colorations are greater betweenbrunneusandinfernatisthan betweenbrunneusandpallidus); 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 ofB. 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) describedbrunneus, 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 thehigher 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 withbrunneus. 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 ofB. m. pallidusto the west in central México. But there is no evidence of gene flow between the paler coastal specimens andB. m. pallidusto 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 distinguishingbrunneusfrom all other subspecies ofB. musculus.Specimens examined.—Total 187 all fromVeracruz, 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.[2]U. S. Nat. Museum (Biol. Surv. Coll.).[3]Chicago Natural History Museum.[4]Univ. Michigan, Museum of Zoology.[5]Texas A & M, Coop. Wildlife Res. Coll.[6]Univ. Illinois, Mus. Nat. History.Baiomys musculus grisescensGoldmanBaiomys musculus griesescensGoldman, Proc. Biol. Soc. Washington, 45:121, July 30, 1932; Ellerman, The Families and Genera of Living Rodents, 2:402, March 21, 1941; Poole and Schantz, Bull. U. S. Nat. Mus., 178:259, March 6, 1942; Goodwin, Bull. Amer. Mus. Nat. Hist., 79(2):160-161, May 29, 1942 (part); Miller and Kellogg, Bull. U. S. Nat. Mus., 205:513, March 3, 1955 (part); Felten, Senck. Biol., 39:136, August 30, 1958; Packard, Univ. Kansas Publs., Mus. Nat. Hist., 9:401, December 19, 1958; Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part).Type.—Adult female, skin and skull; No. 257083 U. S. Nat. Mus. (Biol. Surv. Coll.); Comayabuela [= Comayaguela] just south of Tegucigalpa, 3100 feet, Honduras; obtained on March 6, 1932, by C. F. Underwood, original number 838.[Pg 615]Range.—Central to south-central Guatemala, east to south-central Honduras. Zonal range: Lower parts of the Merendon Biotic Province of Smith (1949:235). Occurs from 3200 feet at a place1/2mi. N and 1 mi. W Salama, Guatemala, up to approximately 4500 feet at Monte Redondo, Guatemala.Diagnosis.—Size medium to small for the species; general ground color of dorsum between Olive Brown and Buffy Brown; distal fourth of individual guard hairs of dorsum black-tipped, proximal three-fourths gray, underfur black-tipped with subterminal band of Vinaceous-Buff, gray basally; facial region below eye Olive-Buff to Deep Olive-Buff; regions of flanks without black-tipped guard hairs, therefore, appearing paler brownish-buff than dorsum; venter Pale Olive-Buff to whitish in midline, hairs there white to base, laterally grayish basally; hairs in region of throat and chin resemble those of underparts; forefeet and hind feet flesh-colored with grayish suffusion; ears dusky brown; tail almost unicolored, slightly darker brown above than below; coronoid process less acutely falcate than in other subspecies; zygoma bowed. Average and extreme external and cranial measurements of 14 adults from La Piedra de Jesús Sabana Grande, Honduras, are as follows: Total length, 110.7 (100-123); length of tail vertebrae, 44.0 (32-55); length of body, 66.7 (60-70); length of hind foot, 14.1 (12-15); length of ear from notch, 11.8 (10-13); occipitonasal length, 19.3 (18.9-19.8); zygomatic breadth, 10.1 (9.8-10.4); postpalatal length, 6.8 (6.2-7.3); least interorbital breadth, 3.9 (3.8-4.1); length of incisive foramina, 4.3 (4.0-4.5); length of rostrum, 6.9 (6.6-7.2); breadth of braincase, 9.6 (9.2-10.1); depth of cranium, 7.0 (6.8-7.3); alveolar length of maxillary tooth-row, 3.2 (3.0-3.4); for photographs of skull, seePlate 1b, andPlate 3b.Comparisons.—For comparisons withB. m. pullusandB. m. handleyi, see accounts of those subspecies. FromB. m. nigrescens,B. m. grisescensdiffers in: dorsum less blackish (dark brown to buffy); face buffy below eye rather than brownish-black; venter buffy to whitish in midline, not sooty gray; forefeet and hind feet flesh-colored with gray overtones, not dusky to sooty; zygoma bowed, sides less parallel; braincase and bony palate slightly broader.Remarks.—Goodwin (1942:160) mentioned that a specimen from the type locality ofgrisescenswas as dark as specimens ofB. m. nigrescensfrom Guatemala. However, all specimens from Guatemala, other than those from Sacapulas, were referred by Goodwin (1934:40) toB. m. nigrescens. My studies reveal a grayish-brown population in central Honduras near to and including the type locality. This population appears to grade into a slightly paler, particularly as concerns color of hind foot and tail, group of Guatemalan mice from 1 mi. S Rabinal, from1/2mi. N, 1 mi. E Salama, and from Lake Atescatempa. Specimens from western Guatemala at Nentón and Jacaltenango, on the other hand, are darker brownish-black, more nearly like the paratypical series ofnigrescensfrom the Valley of Comitán, Chiapas, Republic of México. This darker brownish-black color of the back persists in specimens from southernGuatemala and El Salvador (see specimens examined ofB. m. nigrescensfor localities), and they are best referred tonigrescens.B. m. grisescens, in color and certain cranial characters, therefore, seems to grade into two different subspecies: (1)B. m. handleyi, pale mice in the Río Negro valley in central Guatemala, and (2)B. m. nigrescens, dark mice from southern Guatemala, and parts of El Salvador.Felten (1958:136) referred allB. musculusfrom El Salvador toB. m. grisescens. Although I have not examined the specimens reported on by Felten (loc. cit.), I have examined specimens from Lake Atescatempa, Guatemala (which I refer togrisescens), not too distant from Cerro Blanco, and Finca Las Canarias, Department of Ahuachapan, and Laguna de Guija, Department of Santa Ana (localities listed by Felten). It would seem that specimens from these localities might indeed begrisescens. However, specimens that I examined from 1 mi. S Los Planes, and 1 mi. NW San Salvador were considerably darker than paratypes ofgrisescensand were nearly intermediate in color betweennigrescensandpullus. I refer the specimens from 1 mi. NW San Salvador, and 1 mi. S Los Planes tonigrescensrather than togrisescens.There is no positive evidence thatB. m. grisescensintergrades withB. m. pullusto the south in Nicaragua. But, there is a suggestion that intergradation occurs between these subspecies in a series of 76 skins from La Piedra de Jesús Sabana Grande, Honduras, referable togrisescens. A total of 16 of 76 skins from this locality (21 per cent) possess the mid-ventral white stripe found in 18 of 20 skins (90 per cent), from the type locality ofpullusin Nicaragua. Further collection in areas between central Honduras and western Nicaragua may yield specimens ofB. musculusthat are intermediate in characters betweengrisescensandpullus.Specimens examined.—Total 149, distributed as follows:Guatemala: 1 mi. S Rabinal, 3450 ft., 14;1/2mi. 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 Jesús Sabana Grande, 76[8];Cerro de las Cuches Sabana Grande, 5.Marginal records.—Guatemala:1/2mi. N, 1 mi. E Salama, 3200 ft.Honduras: El Caliche, Cedros; Hatillo; La Piedra de Jesús 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 handleyiPackardBaiomys musculus handleyiPackard, 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 Río 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, seePlate 1c, andPlate 3c.Comparisons.—FromB. m. nigrescens,B. m. handleyidiffers as follows: everywhere paler; forefeet and hind feet whitish instead of dusky to sooty; hairs of anterior part of face white instead of brown; tail bicolored instead of unicolored; anterior tips of nasals truncate rather than rounded; frontoparietal suture forming obtuse angle with suture separating parietals instead of forming right angle; tail and upper molar tooth-row longer.FromB. m. grisescens,B. m. handleyidiffers 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. handleyiseems 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 canyonfor 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. handleyiintergrades withB. m. grisescensto the south. Specimens from 1 mi. S Rabinal, and those from a second locality1/2mi. N and 1 mi. E Salama, Guatemala, are intermediate in color of pelage betweenhandleyiandgrisescens. 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 betweenhandleyiandgrisescens, 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 ofhandleyifrom that ofnigrescensto the north, while to the west the cactus-mesquite habitat ofhandleyigives way to the oak-pine timber that, so far as known, does not supportBaiomys. The difference in elevation and flora seems to restrict gene flow betweenhandleyiand the more northernnigrescens. 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 palehandleyiand blackish-brownnigrescens.The subspecies closest, geographically, toB. m. handleyiisB. m. nigrescens, from whichB. m. handleyidiffers more in color than from any of the other named subspecies, exceptB. 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, fromGuatemala: type locality, including the type: 12 (U. S. Nat. Mus., Biol. Surv. Coll.), 37 (Amer. Mus. Nat. Hist.).Baiomys musculus infernatisHooperBaiomys musculus infernatisHooper, 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.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, seePlate 1d, andPlate 3d.Comparisons.—For comparisons withB. m. nigrescensandB. m. brunneus, see accounts of those subspecies. FromB. m. pallidus,B. m. infernatisdiffers in: sides, ears, and dorsum paler (less of dark brown); venter whitish gray rather than gray with tinge of buff and brown; forefeet and hind feet paler; tail bicolored, not unicolored; incisive foramina longer and not constricted posteriorly; mastoid process turning dorsally and sickle-shaped at posteriormost point rather than capitate.Remarks.—B. m. infernatisresemblesB. m. handleyimore than any other subspecies in color of pelage and in external and cranial dimensions. The resemblance in color betweenB. m. pallidus, in certain parts of its range, andB. m. handleyimay have resulted from nearly parallel selective forces that gave rise to two subspecies, widely separated geographically. The same relation obtains betweenB. m. infernatisandB. m. handleyi. Both inhabit arid river basins. In them, pale soil and low relative humidity are important passive factors of selection that give adaptive value to the pale colors of pelage of bothinfernatisandhandleyi.Specimens from 61/2mi. SW Izucár de Matemores, and 1 mi. SSW Tilapa, Puebla, are intergrades betweenB. m. infernatisandB. m.pallidus. These specimens are intermediate in color and cranial characters between the aforementioned subspecies but possess more of the pale brown overtones seen in paratypes ofpallidus, and are best referred to that subspecies.Specimens examined(All in Univ. Michigan, Mus. Zool.).—Total 18, all from the Republic of México and distributed as follows:Puebla, Tepanaco, 6000 ft., 3, Tehuacán, 5400 ft., 3.Oaxaca: Type locality, 3100 ft., 12 (including the type).Marginal records.—See specimens examined.Baiomys musculus musculus(Merriam)Sitomys musculusMerriam, Proc. Biol. Soc. Washington, 7:170, September 29, 1892; Lyon and Osgood, Bull. U. S. Nat. Mus., 62:135, January 15, 1909.Baiomys musculus[=musculus], Mearns, Bull. U. S. Nat. Mus., 56:381, April 13, 1907; Hooper, Jour. Mamm., 36:29, May 26, 1955.Peromyscus musculus[musculus], J. A. Allen and Chapman, Bull. Amer. Mus. Nat. Hist., 9:203, June 16, 1897; Elliot, Field Columb. Mus. Publ., 105(4):135, July 1, 1905; Osgood, N. Amer. Fauna, 28:257, April 17, 1909 (part).[Peromyscus]musculus, Trouessart, Cat. Mamm., 1:518, 1898.[Peromyscus]musculus[musculus], Elliot, Field Columb. Mus. Publ., 95(4):175, July 15, 1904.Baiomys musculus musculus, Miller, Bull. U. S. Nat. Mus., 79:137, December 31, 1912 (part); Miller, Bull. U. S. Nat. Mus., 128:318, April 29, 1924 (part); Ellerman, The Families and Genera of Living Rodents, 2:402, March 21, 1941; Poole and Schantz, Bull. U. S. Nat. Mus., 178:258, March 6, 1942; Davis, Jour. Mamm., 25:394, December 12, 1944 (part); Hooper, Jour. Mamm., 28:50, February 15, 1947 (part); 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); Goldman, Smith. Miscl. Coll., 115:336, July 31, 1951 (part); Miller and Kellogg, Bull. U. S. Nat. Mus., 205:512, March 3, 1955 (part); Hooper, Occas. Papers Mus. Zool. Univ. Michigan, 565:13, March 31, 1955; Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part).B.[aiomys]m.[usculus]musculus, Hooper, Jour. Mamm., 33:97, February 18, 1952 (part); Packard, Univ. Kansas Publs., Mus. Nat. Hist., 9:400; December 19, 1958.Baiomys taylori allex, Hall and Kelson, The Mammals of North America, 2:659, March 31, 1959 (part).Type.—Adult female, skin and skull; No. 33437/45460 U. S. Nat. Mus. (Biol. Surv. Coll.); Colima (City), Colima, Republic of México, obtained on March 9, 1892, by E. W. Nelson, original number 2055.Range.—Southwestern Nayarit and northwestern Jalisco, south into Colima, thence eastward into Michoacán. Zonal range: part of arid Lower Tropical Subzone of Goldman (1951:330); approximates part of the Nayarit-Guerrero Biotic Province of Goldman and Moore (1945:349). Occurs from near sea level in Colima up to 5800 feet in Jalisco.Diagnosis.—Size large for the species; dorsum Olive-Brown in darkest series to Buffy Brown with tones of Fawn Color in the palest series; guard[Pg 621]hairs of dorsum black-tipped, gray basally (in some specimens, guard hairs gray-tipped with subterminal black band, and gray base); underfur of dorsum black-tipped with subterminal band of fawn to buff, Neutral Gray basally; face and head paler than back because of greater number of fawn-colored and buff-colored hairs; hairs on throat and chin white to base; venter and flanks Pale Olive-Buff in palest series to Gray (Pale Gull Gray) in darkest series; individual hairs of venter tipped with white to buff, basally Gray (Dark Gull Gray); forefeet and hind feet white to gray with flesh-colored undertones; tail faintly bicolored, individual hairs above black, below white; nasals flared anteriorly; zygoma and zygomatic plate thick. Average and extreme external and cranial measurements for 8 adults from Armeria, Colima, are as follows: total length, 125.5 (115-135); length of tail vertebrae, 47.5 (42-54); length of body, 75.6 (68-81); length of hind foot, 16.5 (16-17); occipitonasal length, 20.3 (19.8-20.7); zygomatic breadth, 10.7 (10.3-11.1); postpalatal length, 7.4 (7.1-7.7); least interorbital breadth, 4.0 (3.9-4.1); length of incisive foramina, 4.3 (4.1-4.5); length of rostrum, 7.3 (6.9-7.6); breadth of braincase, 9.8 (9.4-10.0); depth of cranium, 7.1 (6.7-7.2); alveolar length of maxillary tooth-row, 3.4 (3.3-3.6); for photographs of skull, seePlate 1e, andPlate 3e.Comparisons.—For comparisons withB. m. brunneus,B. m. infernatis, andB. m. pallidus, see accounts of those subspecies. FromB. m. nigrescens,B. m. musculusdiffers in: dorsum paler throughout (less of blackish brown); region of face and ears paler, more buff and fawn-colored hairs rather than blackish-brown to grayish hairs; vibrissae paler; venter paler, less dark gray and less of sooty-colored undertones, tips of hairs whitish to pale Olive-Buff rather than light gray at tips becoming darker basally; forefeet and hind feet paler, whitish to pale buff-color with flesh-colored undertones, not sooty-colored to dark brown; tail paler below; nasals flaring outward, not tapering toward midline at anteriormost point; zygoma more massive; larger in external and cranial dimensions.Remarks.—Merriam (1892:170) describedSitomys[=Baiomys]musculuson the basis of 23 specimens (from Colima City, Colima; Armeria, Colima; Plantinar, and Zapotlán, Jalisco). According to the original description,B. musculusresembled a small house mouse and was smaller than any known species ofSitomysexceptS. taylori[=Baiomys taylori]. Fromtaylori,musculusdiffered in being larger [in size of body], and in having longer ears and tail, and larger hind feet. When Allen and Chapman (1897:203) describedPeromyscus[=Baiomys]musculus brunneusfrom Jalapa, Veracruz, the specimens described by Merriam from Colima and Jalisco became representative of the nominal subspeciesB. m. musculus. Osgood (1909:258) assigned specimens from Colima, Guerrero, Jalisco, Michoacán, Morelos, Oaxaca, Puebla, Sinaloa, Veracruz, and Zacatecas to the subspeciesmusculus. Subsequently, Russell (1952:21) named the subspeciespallidusfrom the arid lowlands of Morelos; Hooper (1952:96) described the subspeciesinfernatisfrom northern Oaxaca and southeastern Puebla; and Goodwin (1959:1) described a new subspeciesnebulosusfrom the Oaxaca highlands. Each of the subspecies mentioned immediately above was described from within the geographic range assigned toB. m. musculusby Osgood (loc. cit.). Hall and Kelson (1959:661) mapped the range ofB. m. musculusso as to include Colima, parts of Jalisco, Michoacán, Guerrero, Oaxaca, and Veracruz. Lukens (1955:159), in a study of the mammals of Guerrero, has shown that the characters attributed toB. m. pallidusare not significantly different from those of pygmy mice studied from Guerrero. He (loc. cit.) concluded that: (1) if the specimens of pygmy mice from central Guerrero were typical of the subspeciesmusculus, thenpallidusdid not deserve subspecific recognition, or; (2) the nameB. m. musculusshould be restricted to the larger pygmy mice inhabiting the lowlands immediately adjacent to the Pacific Coast and the area to the north. My data (seeFigure 12) show pygmy mice from southwestern Nayarit, northwestern and central Jalisco, Colima, and parts of Michoacán to be significantly larger in certain cranial and external measurements than pygmy mice from Guerrero, Oaxaca, Morelos, and parts of Puebla. This finding essentially corroborates Hooper's (1952a:96) findings. It seems advisable, therefore, to restrict the range ofB. musculus musculusto the large mice inhabiting west-central México and the coastal lowlands of Colima and Michoacán. The namepallidusis applicable to the smaller mice occupying Morelos, southwestern Puebla, Guerrero, Oaxaca, and southwestern Chiapas.B. m. musculusintergrades withB. m. pallidusin eastern Michoacán and central and western Guerrero. Specimens from San José Prura and 12 mi. S Tzitzio, Michoacán, though referable toB. m. musculusbecause of slightly larger size of crania are intermediate in size and color between the smaller and slightly darkerpallidusto the south and east and the larger, slightly palermusculusto the northwest.Specimens examined.—Total 156 all from the Republic of México, and distributed as follows:Nayarit: 3 mi. NNW Las Varas, 150 ft., 1.Jalisco: 7 mi. W Ameca, 4000 ft., 2[10];6 mi. W Ameca, 4300 ft., 3[10];10 mi. S Ameca, 5800 ft., 1[10];13 mi. S, 15 mi. W Guadalajara, 3;13 mi. S, 91/2mi. W Guadalajara, 1;3 mi. ENE Santa Cruz de las Flores, 1; 27 mi. S, 12 mi. W Guadalajara, 1;4 mi. NE Autlán, 3000 ft., 5[10];Sierra de Autlán, 5000 ft., 2[10];21/2mi. NNE Autlán, 3000 ft., 8; 2 mi. SSE Autlán, 1;5 mi. S Purificación, 2; Chamela Bay, 1[10];2 mi. N La Resolana, 1500 ft., 6[10];1 mi. N San Gabriel, 4000 ft., 32[10]; 2 mi. N Cuidad Guzmán, 5000 ft., 1; 3 mi. E Navidad, 4300 ft., 10[10].Colima:type locality, 10[11](including the type);3 mi. SE Colima(City), 5[10];4 mi. SW Colima City, 1; Armeria, 200 ft., 8[11];Paso del Río, 20[10].[Pg 623]Michoacán: 12 mi. S Tzitzio, 6[10]; San José Prura, 4[12]; 1 mi. E, 6 mi. S Tacámbaro, 4000 ft., 3[13]; La Salada, 3[11];1/2mi. SE Coalcomán, 15[10].Marginal records.—Nayarit: 3 mi. NNW Las Varas, 150 ft.Jalisco: 3 mi. E Navidad, 4300 ft.; 27 mi. S, 12 mi. W Guadalajara.Michoacán: 12 mi. S Tzitzio; San José Prura;1/2mi. SE Coalcomán.Colima: Armeria, 200 ft.Jalisco: Chamela Bay.

Natural History

Habitat and numbers.—In Veracruz, Dalquest obtained the southern pygmy mouse in stands of tall grass (Spartina?) in sandy loam soil bordering, and in, dense vegetation; Davis (1944:394) found the species living in dense stands of grasses and seemingly utilizing underground burrows. Near Chilpancingo, Guerrero, rocky situations seemed to be the preferred habitat. Davis (loc. cit.) believedthat the species has a wide tolerance to kinds of habitats. In Morelos, Davis and Russell (1954:75) found these mice to be abundant along rock fences separating cultivated fields, and in arid lowlands. In Colima, Hooper (1955b:13) obtained specimens from an open thorn forest in sparse grass and rocky hillside bounding a stream and in litter below shrubs on the floor of a nut-palm forest; in Michoacán, these mice were taken in cane grass, shrubs, and mesquite near an irrigation ditch. From Guatemala, Goodwin (1934:39, 40) records specimens from Sacapulas, a hot, dry, sandy area where cactus and sparse grasses are present, and from La Primavera, on the edges of pine-oak-alder forests. Felten (1958:137) has takenmusculusfrom bushy areas in El Salvadore. In 1955, I obtained the southern pygmy mouse 6 mi. SW Izucár de Matemores, Puebla, along a stream in heavy grass bordered by cypress, willow, fig, bamboo, and in rocky grazed area near sugar cane fields.

The southern pygmy mouse seems to be locally abundant in certain parts of its geographic range, and in other parts, scarce. For example, Dalquest (in. litt.) recorded the pygmy mouse as common at a place 2 km. N Paraje Nuevo, 1700 feet, Veracruz, where, by means of 50 traps, he took 14 of these mice in one night. The species was scarcer, although the habitat seemed suitable, 3 km. N Presidio, 1500 feet, Veracruz, where he caught only two pygmy mice in several days of trapping. Six miles southwest of Izucár de Matemores, the pygmy mouse was the most common rodent. I have trapped for it in Oaxaca and Veracruz in habitats that seemed almost identical to those mentioned by Dalquest, and also that at Izucár de Matemores, Puebla, with almost no success. The reason for the seeming disparity in numbers at different localities having nearly the same kind of habitat is unknown to me and bears further investigation.

Behavior.—Little is recorded concerning the behavior of this species. David and Russell (op. cit.:76) found that of small mammalsB. musculuswas the first to appear at night. I caught mice of this species by hand in the afternoon in Puebla. They seemed to be active from noon until dark. Albert Alcorn wrote in his field notes that specimens were taken near noon at a place 9 mi. NNW Estelí, Nicaragua. My impression is thatmusculusis diurnal to crepuscular.

Enemies and food.—Owl pellets (thought to be those of a barn owl,Tyto alba) from within the geographic range ofB. musculus, from 6 mi. SW Izucár de Matemores, yielded mandibular tooth-rows belonging tomusculus. Presumably, most of the carnivorous mammalsand raptorial birds within the range of the southern pygmy mouse could be listed as enemies. Diurnal to crepuscular habits of this mouse may protect it from some of the nocturnal carnivorous mammals and raptorial birds.

Food of the southern pygmy mouse includes nuts, bark, grass seeds, and leaves. Dalquest (MS) writes that bits of banana proved to be useful bait in trapping these mice in Veracruz.

Reproduction.—Notations concerning lactation and embryos on specimen labels of females suggest that the southern pygmy mouse breeds in all months. I have records of pregnant or lactating females in every month, save January, April, May, and June. The average of 26 counts of embryos or young per litter is 2.92 (1-4).

Baiomys musculus brunneus(J. A. Allen and Chapman)

Peromyscus musculus brunneusJ. A. Allen and Chapman, Bull. Amer. Mus. Nat. Hist., 9:203, June 16, 1897; Elliott, Field Columb. Mus. Publ., 105(4):136, July 1, 1905; Elliott, Field Columb. Mus. Publ., 115(8):203, 1907; Osgood, N. Amer. Fauna, 28:259, April 17, 1909.

Baiomys musculus brunneus, Miller, Bull. U. S. Nat. Mus., 79:137, December 31, 1912; Miller, Bull. U. S. Nat. Mus., 128:318, April 29, 1924; Ellerman, The Families and Genera of Living Rodents, 2:402, March 21, 1941; Goldman, Smith. Miscl. Coll., 115:437, July 31, 1951; Goodwin, Bull. Amer. Mus. Nat. Hist., 102:318, August 31, 1953; Miller and Kellogg, Bull. U. S. Nat. Mus., 205:512, March 3, 1955; Booth, Walla Walla Publs., Dept. Biol. Sci., 20:15, July 10, 1957; Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part).

[Peromyscus musculus]brunneus, Elliott, Field Columb. Mus. Publ., 95(4): 176, 1904.

Baiomys musculus musculus, Davis, Jour. Mamm., 25:394, December 12, 1944 (part); Goldman, Smith Miscl. Coll., 115:437, July 31, 1951; Hooper, Jour. Mamm., 33:97, February 18, 1952 (part); Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part).

B.[aiomys]m.[usculus]brunneus, Hooper, Jour. Mamm., 33:96, February 18, 1952.

Baiomys taylori, Hooper, Jour. Mamm., 33:97, February 18, 1952 (part).

Type.—Adult female, skin and skull; No. 12535/10845 American Museum of Natural History; Jalapa, Veracruz, Republic of México; obtained on April 13, 1897, by F. M. Chapman, original number 1203.Range.—Central Veracruz, coastal plains and eastern slopes of the plateau of Central México, seeFigure 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, seePlate 1a, andPlate 3a.Comparisons.—For comparisons withB. m. nigrescens, see account of that subspecies. FromB. m. pallidus,B. m. brunneusdiffers 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.FromB. m. infernatis,B. m. brunneusdiffers in: side of face and neck deep reddish-brown rather than yellowish-gray (the differences in dorsal colorations are greater betweenbrunneusandinfernatisthan betweenbrunneusandpallidus); 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.

Type.—Adult female, skin and skull; No. 12535/10845 American Museum of Natural History; Jalapa, Veracruz, Republic of México; obtained on April 13, 1897, by F. M. Chapman, original number 1203.

Range.—Central Veracruz, coastal plains and eastern slopes of the plateau of Central México, seeFigure 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, seePlate 1a, andPlate 3a.

Comparisons.—For comparisons withB. m. nigrescens, see account of that subspecies. FromB. m. pallidus,B. m. brunneusdiffers 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.

FromB. m. infernatis,B. m. brunneusdiffers in: side of face and neck deep reddish-brown rather than yellowish-gray (the differences in dorsal colorations are greater betweenbrunneusandinfernatisthan betweenbrunneusandpallidus); 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 ofB. 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) describedbrunneus, 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 thehigher 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 withbrunneus. 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 ofB. m. pallidusto the west in central México. But there is no evidence of gene flow between the paler coastal specimens andB. m. pallidusto 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 distinguishingbrunneusfrom all other subspecies ofB. musculus.

Specimens examined.—Total 187 all fromVeracruz, 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.

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.

[2]U. S. Nat. Museum (Biol. Surv. Coll.).

[3]Chicago Natural History Museum.

[4]Univ. Michigan, Museum of Zoology.

[5]Texas A & M, Coop. Wildlife Res. Coll.

[6]Univ. Illinois, Mus. Nat. History.

Baiomys musculus grisescensGoldman

Baiomys musculus griesescensGoldman, Proc. Biol. Soc. Washington, 45:121, July 30, 1932; Ellerman, The Families and Genera of Living Rodents, 2:402, March 21, 1941; Poole and Schantz, Bull. U. S. Nat. Mus., 178:259, March 6, 1942; Goodwin, Bull. Amer. Mus. Nat. Hist., 79(2):160-161, May 29, 1942 (part); Miller and Kellogg, Bull. U. S. Nat. Mus., 205:513, March 3, 1955 (part); Felten, Senck. Biol., 39:136, August 30, 1958; Packard, Univ. Kansas Publs., Mus. Nat. Hist., 9:401, December 19, 1958; Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part).

Type.—Adult female, skin and skull; No. 257083 U. S. Nat. Mus. (Biol. Surv. Coll.); Comayabuela [= Comayaguela] just south of Tegucigalpa, 3100 feet, Honduras; obtained on March 6, 1932, by C. F. Underwood, original number 838.[Pg 615]Range.—Central to south-central Guatemala, east to south-central Honduras. Zonal range: Lower parts of the Merendon Biotic Province of Smith (1949:235). Occurs from 3200 feet at a place1/2mi. N and 1 mi. W Salama, Guatemala, up to approximately 4500 feet at Monte Redondo, Guatemala.Diagnosis.—Size medium to small for the species; general ground color of dorsum between Olive Brown and Buffy Brown; distal fourth of individual guard hairs of dorsum black-tipped, proximal three-fourths gray, underfur black-tipped with subterminal band of Vinaceous-Buff, gray basally; facial region below eye Olive-Buff to Deep Olive-Buff; regions of flanks without black-tipped guard hairs, therefore, appearing paler brownish-buff than dorsum; venter Pale Olive-Buff to whitish in midline, hairs there white to base, laterally grayish basally; hairs in region of throat and chin resemble those of underparts; forefeet and hind feet flesh-colored with grayish suffusion; ears dusky brown; tail almost unicolored, slightly darker brown above than below; coronoid process less acutely falcate than in other subspecies; zygoma bowed. Average and extreme external and cranial measurements of 14 adults from La Piedra de Jesús Sabana Grande, Honduras, are as follows: Total length, 110.7 (100-123); length of tail vertebrae, 44.0 (32-55); length of body, 66.7 (60-70); length of hind foot, 14.1 (12-15); length of ear from notch, 11.8 (10-13); occipitonasal length, 19.3 (18.9-19.8); zygomatic breadth, 10.1 (9.8-10.4); postpalatal length, 6.8 (6.2-7.3); least interorbital breadth, 3.9 (3.8-4.1); length of incisive foramina, 4.3 (4.0-4.5); length of rostrum, 6.9 (6.6-7.2); breadth of braincase, 9.6 (9.2-10.1); depth of cranium, 7.0 (6.8-7.3); alveolar length of maxillary tooth-row, 3.2 (3.0-3.4); for photographs of skull, seePlate 1b, andPlate 3b.Comparisons.—For comparisons withB. m. pullusandB. m. handleyi, see accounts of those subspecies. FromB. m. nigrescens,B. m. grisescensdiffers in: dorsum less blackish (dark brown to buffy); face buffy below eye rather than brownish-black; venter buffy to whitish in midline, not sooty gray; forefeet and hind feet flesh-colored with gray overtones, not dusky to sooty; zygoma bowed, sides less parallel; braincase and bony palate slightly broader.

[Pg 615]

Range.—Central to south-central Guatemala, east to south-central Honduras. Zonal range: Lower parts of the Merendon Biotic Province of Smith (1949:235). Occurs from 3200 feet at a place1/2mi. N and 1 mi. W Salama, Guatemala, up to approximately 4500 feet at Monte Redondo, Guatemala.

Diagnosis.—Size medium to small for the species; general ground color of dorsum between Olive Brown and Buffy Brown; distal fourth of individual guard hairs of dorsum black-tipped, proximal three-fourths gray, underfur black-tipped with subterminal band of Vinaceous-Buff, gray basally; facial region below eye Olive-Buff to Deep Olive-Buff; regions of flanks without black-tipped guard hairs, therefore, appearing paler brownish-buff than dorsum; venter Pale Olive-Buff to whitish in midline, hairs there white to base, laterally grayish basally; hairs in region of throat and chin resemble those of underparts; forefeet and hind feet flesh-colored with grayish suffusion; ears dusky brown; tail almost unicolored, slightly darker brown above than below; coronoid process less acutely falcate than in other subspecies; zygoma bowed. Average and extreme external and cranial measurements of 14 adults from La Piedra de Jesús Sabana Grande, Honduras, are as follows: Total length, 110.7 (100-123); length of tail vertebrae, 44.0 (32-55); length of body, 66.7 (60-70); length of hind foot, 14.1 (12-15); length of ear from notch, 11.8 (10-13); occipitonasal length, 19.3 (18.9-19.8); zygomatic breadth, 10.1 (9.8-10.4); postpalatal length, 6.8 (6.2-7.3); least interorbital breadth, 3.9 (3.8-4.1); length of incisive foramina, 4.3 (4.0-4.5); length of rostrum, 6.9 (6.6-7.2); breadth of braincase, 9.6 (9.2-10.1); depth of cranium, 7.0 (6.8-7.3); alveolar length of maxillary tooth-row, 3.2 (3.0-3.4); for photographs of skull, seePlate 1b, andPlate 3b.

Comparisons.—For comparisons withB. m. pullusandB. m. handleyi, see accounts of those subspecies. FromB. m. nigrescens,B. m. grisescensdiffers in: dorsum less blackish (dark brown to buffy); face buffy below eye rather than brownish-black; venter buffy to whitish in midline, not sooty gray; forefeet and hind feet flesh-colored with gray overtones, not dusky to sooty; zygoma bowed, sides less parallel; braincase and bony palate slightly broader.

Remarks.—Goodwin (1942:160) mentioned that a specimen from the type locality ofgrisescenswas as dark as specimens ofB. m. nigrescensfrom Guatemala. However, all specimens from Guatemala, other than those from Sacapulas, were referred by Goodwin (1934:40) toB. m. nigrescens. My studies reveal a grayish-brown population in central Honduras near to and including the type locality. This population appears to grade into a slightly paler, particularly as concerns color of hind foot and tail, group of Guatemalan mice from 1 mi. S Rabinal, from1/2mi. N, 1 mi. E Salama, and from Lake Atescatempa. Specimens from western Guatemala at Nentón and Jacaltenango, on the other hand, are darker brownish-black, more nearly like the paratypical series ofnigrescensfrom the Valley of Comitán, Chiapas, Republic of México. This darker brownish-black color of the back persists in specimens from southernGuatemala and El Salvador (see specimens examined ofB. m. nigrescensfor localities), and they are best referred tonigrescens.B. m. grisescens, in color and certain cranial characters, therefore, seems to grade into two different subspecies: (1)B. m. handleyi, pale mice in the Río Negro valley in central Guatemala, and (2)B. m. nigrescens, dark mice from southern Guatemala, and parts of El Salvador.

Felten (1958:136) referred allB. musculusfrom El Salvador toB. m. grisescens. Although I have not examined the specimens reported on by Felten (loc. cit.), I have examined specimens from Lake Atescatempa, Guatemala (which I refer togrisescens), not too distant from Cerro Blanco, and Finca Las Canarias, Department of Ahuachapan, and Laguna de Guija, Department of Santa Ana (localities listed by Felten). It would seem that specimens from these localities might indeed begrisescens. However, specimens that I examined from 1 mi. S Los Planes, and 1 mi. NW San Salvador were considerably darker than paratypes ofgrisescensand were nearly intermediate in color betweennigrescensandpullus. I refer the specimens from 1 mi. NW San Salvador, and 1 mi. S Los Planes tonigrescensrather than togrisescens.

There is no positive evidence thatB. m. grisescensintergrades withB. m. pullusto the south in Nicaragua. But, there is a suggestion that intergradation occurs between these subspecies in a series of 76 skins from La Piedra de Jesús Sabana Grande, Honduras, referable togrisescens. A total of 16 of 76 skins from this locality (21 per cent) possess the mid-ventral white stripe found in 18 of 20 skins (90 per cent), from the type locality ofpullusin Nicaragua. Further collection in areas between central Honduras and western Nicaragua may yield specimens ofB. musculusthat are intermediate in characters betweengrisescensandpullus.

Specimens examined.—Total 149, distributed as follows:Guatemala: 1 mi. S Rabinal, 3450 ft., 14;1/2mi. 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 Jesús Sabana Grande, 76[8];Cerro de las Cuches Sabana Grande, 5.Marginal records.—Guatemala:1/2mi. N, 1 mi. E Salama, 3200 ft.Honduras: El Caliche, Cedros; Hatillo; La Piedra de Jesús Sabana Grande; Cementario.Guatemala: Lake Atescatempa; 1 mi. S Rabinal, 3450 ft.

Marginal records.—Guatemala:1/2mi. N, 1 mi. E Salama, 3200 ft.Honduras: El Caliche, Cedros; Hatillo; La Piedra de Jesús 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 handleyiPackard

Baiomys musculus handleyiPackard, 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 Río 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, seePlate 1c, andPlate 3c.Comparisons.—FromB. m. nigrescens,B. m. handleyidiffers as follows: everywhere paler; forefeet and hind feet whitish instead of dusky to sooty; hairs of anterior part of face white instead of brown; tail bicolored instead of unicolored; anterior tips of nasals truncate rather than rounded; frontoparietal suture forming obtuse angle with suture separating parietals instead of forming right angle; tail and upper molar tooth-row longer.FromB. m. grisescens,B. m. handleyidiffers 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.

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 Río 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, seePlate 1c, andPlate 3c.

Comparisons.—FromB. m. nigrescens,B. m. handleyidiffers as follows: everywhere paler; forefeet and hind feet whitish instead of dusky to sooty; hairs of anterior part of face white instead of brown; tail bicolored instead of unicolored; anterior tips of nasals truncate rather than rounded; frontoparietal suture forming obtuse angle with suture separating parietals instead of forming right angle; tail and upper molar tooth-row longer.

FromB. m. grisescens,B. m. handleyidiffers 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. handleyiseems 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 canyonfor 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. handleyiintergrades withB. m. grisescensto the south. Specimens from 1 mi. S Rabinal, and those from a second locality1/2mi. N and 1 mi. E Salama, Guatemala, are intermediate in color of pelage betweenhandleyiandgrisescens. 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 betweenhandleyiandgrisescens, 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 ofhandleyifrom that ofnigrescensto the north, while to the west the cactus-mesquite habitat ofhandleyigives way to the oak-pine timber that, so far as known, does not supportBaiomys. The difference in elevation and flora seems to restrict gene flow betweenhandleyiand the more northernnigrescens. 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 palehandleyiand blackish-brownnigrescens.

The subspecies closest, geographically, toB. m. handleyiisB. m. nigrescens, from whichB. m. handleyidiffers more in color than from any of the other named subspecies, exceptB. 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, fromGuatemala: type locality, including the type: 12 (U. S. Nat. Mus., Biol. Surv. Coll.), 37 (Amer. Mus. Nat. Hist.).

Baiomys musculus infernatisHooper

Baiomys musculus infernatisHooper, 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.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, seePlate 1d, andPlate 3d.Comparisons.—For comparisons withB. m. nigrescensandB. m. brunneus, see accounts of those subspecies. FromB. m. pallidus,B. m. infernatisdiffers in: sides, ears, and dorsum paler (less of dark brown); venter whitish gray rather than gray with tinge of buff and brown; forefeet and hind feet paler; tail bicolored, not unicolored; incisive foramina longer and not constricted posteriorly; mastoid process turning dorsally and sickle-shaped at posteriormost point rather than capitate.

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.

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, seePlate 1d, andPlate 3d.

Comparisons.—For comparisons withB. m. nigrescensandB. m. brunneus, see accounts of those subspecies. FromB. m. pallidus,B. m. infernatisdiffers in: sides, ears, and dorsum paler (less of dark brown); venter whitish gray rather than gray with tinge of buff and brown; forefeet and hind feet paler; tail bicolored, not unicolored; incisive foramina longer and not constricted posteriorly; mastoid process turning dorsally and sickle-shaped at posteriormost point rather than capitate.

Remarks.—B. m. infernatisresemblesB. m. handleyimore than any other subspecies in color of pelage and in external and cranial dimensions. The resemblance in color betweenB. m. pallidus, in certain parts of its range, andB. m. handleyimay have resulted from nearly parallel selective forces that gave rise to two subspecies, widely separated geographically. The same relation obtains betweenB. m. infernatisandB. m. handleyi. Both inhabit arid river basins. In them, pale soil and low relative humidity are important passive factors of selection that give adaptive value to the pale colors of pelage of bothinfernatisandhandleyi.

Specimens from 61/2mi. SW Izucár de Matemores, and 1 mi. SSW Tilapa, Puebla, are intergrades betweenB. m. infernatisandB. m.pallidus. These specimens are intermediate in color and cranial characters between the aforementioned subspecies but possess more of the pale brown overtones seen in paratypes ofpallidus, and are best referred to that subspecies.

Specimens examined(All in Univ. Michigan, Mus. Zool.).—Total 18, all from the Republic of México and distributed as follows:Puebla, Tepanaco, 6000 ft., 3, Tehuacán, 5400 ft., 3.Oaxaca: Type locality, 3100 ft., 12 (including the type).Marginal records.—See specimens examined.

Marginal records.—See specimens examined.

Baiomys musculus musculus(Merriam)

Sitomys musculusMerriam, Proc. Biol. Soc. Washington, 7:170, September 29, 1892; Lyon and Osgood, Bull. U. S. Nat. Mus., 62:135, January 15, 1909.

Baiomys musculus[=musculus], Mearns, Bull. U. S. Nat. Mus., 56:381, April 13, 1907; Hooper, Jour. Mamm., 36:29, May 26, 1955.

Peromyscus musculus[musculus], J. A. Allen and Chapman, Bull. Amer. Mus. Nat. Hist., 9:203, June 16, 1897; Elliot, Field Columb. Mus. Publ., 105(4):135, July 1, 1905; Osgood, N. Amer. Fauna, 28:257, April 17, 1909 (part).

[Peromyscus]musculus, Trouessart, Cat. Mamm., 1:518, 1898.

[Peromyscus]musculus[musculus], Elliot, Field Columb. Mus. Publ., 95(4):175, July 15, 1904.

Baiomys musculus musculus, Miller, Bull. U. S. Nat. Mus., 79:137, December 31, 1912 (part); Miller, Bull. U. S. Nat. Mus., 128:318, April 29, 1924 (part); Ellerman, The Families and Genera of Living Rodents, 2:402, March 21, 1941; Poole and Schantz, Bull. U. S. Nat. Mus., 178:258, March 6, 1942; Davis, Jour. Mamm., 25:394, December 12, 1944 (part); Hooper, Jour. Mamm., 28:50, February 15, 1947 (part); 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); Goldman, Smith. Miscl. Coll., 115:336, July 31, 1951 (part); Miller and Kellogg, Bull. U. S. Nat. Mus., 205:512, March 3, 1955 (part); Hooper, Occas. Papers Mus. Zool. Univ. Michigan, 565:13, March 31, 1955; Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part).

B.[aiomys]m.[usculus]musculus, Hooper, Jour. Mamm., 33:97, February 18, 1952 (part); Packard, Univ. Kansas Publs., Mus. Nat. Hist., 9:400; December 19, 1958.

Baiomys taylori allex, Hall and Kelson, The Mammals of North America, 2:659, March 31, 1959 (part).

Type.—Adult female, skin and skull; No. 33437/45460 U. S. Nat. Mus. (Biol. Surv. Coll.); Colima (City), Colima, Republic of México, obtained on March 9, 1892, by E. W. Nelson, original number 2055.Range.—Southwestern Nayarit and northwestern Jalisco, south into Colima, thence eastward into Michoacán. Zonal range: part of arid Lower Tropical Subzone of Goldman (1951:330); approximates part of the Nayarit-Guerrero Biotic Province of Goldman and Moore (1945:349). Occurs from near sea level in Colima up to 5800 feet in Jalisco.Diagnosis.—Size large for the species; dorsum Olive-Brown in darkest series to Buffy Brown with tones of Fawn Color in the palest series; guard[Pg 621]hairs of dorsum black-tipped, gray basally (in some specimens, guard hairs gray-tipped with subterminal black band, and gray base); underfur of dorsum black-tipped with subterminal band of fawn to buff, Neutral Gray basally; face and head paler than back because of greater number of fawn-colored and buff-colored hairs; hairs on throat and chin white to base; venter and flanks Pale Olive-Buff in palest series to Gray (Pale Gull Gray) in darkest series; individual hairs of venter tipped with white to buff, basally Gray (Dark Gull Gray); forefeet and hind feet white to gray with flesh-colored undertones; tail faintly bicolored, individual hairs above black, below white; nasals flared anteriorly; zygoma and zygomatic plate thick. Average and extreme external and cranial measurements for 8 adults from Armeria, Colima, are as follows: total length, 125.5 (115-135); length of tail vertebrae, 47.5 (42-54); length of body, 75.6 (68-81); length of hind foot, 16.5 (16-17); occipitonasal length, 20.3 (19.8-20.7); zygomatic breadth, 10.7 (10.3-11.1); postpalatal length, 7.4 (7.1-7.7); least interorbital breadth, 4.0 (3.9-4.1); length of incisive foramina, 4.3 (4.1-4.5); length of rostrum, 7.3 (6.9-7.6); breadth of braincase, 9.8 (9.4-10.0); depth of cranium, 7.1 (6.7-7.2); alveolar length of maxillary tooth-row, 3.4 (3.3-3.6); for photographs of skull, seePlate 1e, andPlate 3e.Comparisons.—For comparisons withB. m. brunneus,B. m. infernatis, andB. m. pallidus, see accounts of those subspecies. FromB. m. nigrescens,B. m. musculusdiffers in: dorsum paler throughout (less of blackish brown); region of face and ears paler, more buff and fawn-colored hairs rather than blackish-brown to grayish hairs; vibrissae paler; venter paler, less dark gray and less of sooty-colored undertones, tips of hairs whitish to pale Olive-Buff rather than light gray at tips becoming darker basally; forefeet and hind feet paler, whitish to pale buff-color with flesh-colored undertones, not sooty-colored to dark brown; tail paler below; nasals flaring outward, not tapering toward midline at anteriormost point; zygoma more massive; larger in external and cranial dimensions.

Range.—Southwestern Nayarit and northwestern Jalisco, south into Colima, thence eastward into Michoacán. Zonal range: part of arid Lower Tropical Subzone of Goldman (1951:330); approximates part of the Nayarit-Guerrero Biotic Province of Goldman and Moore (1945:349). Occurs from near sea level in Colima up to 5800 feet in Jalisco.

Diagnosis.—Size large for the species; dorsum Olive-Brown in darkest series to Buffy Brown with tones of Fawn Color in the palest series; guard[Pg 621]hairs of dorsum black-tipped, gray basally (in some specimens, guard hairs gray-tipped with subterminal black band, and gray base); underfur of dorsum black-tipped with subterminal band of fawn to buff, Neutral Gray basally; face and head paler than back because of greater number of fawn-colored and buff-colored hairs; hairs on throat and chin white to base; venter and flanks Pale Olive-Buff in palest series to Gray (Pale Gull Gray) in darkest series; individual hairs of venter tipped with white to buff, basally Gray (Dark Gull Gray); forefeet and hind feet white to gray with flesh-colored undertones; tail faintly bicolored, individual hairs above black, below white; nasals flared anteriorly; zygoma and zygomatic plate thick. Average and extreme external and cranial measurements for 8 adults from Armeria, Colima, are as follows: total length, 125.5 (115-135); length of tail vertebrae, 47.5 (42-54); length of body, 75.6 (68-81); length of hind foot, 16.5 (16-17); occipitonasal length, 20.3 (19.8-20.7); zygomatic breadth, 10.7 (10.3-11.1); postpalatal length, 7.4 (7.1-7.7); least interorbital breadth, 4.0 (3.9-4.1); length of incisive foramina, 4.3 (4.1-4.5); length of rostrum, 7.3 (6.9-7.6); breadth of braincase, 9.8 (9.4-10.0); depth of cranium, 7.1 (6.7-7.2); alveolar length of maxillary tooth-row, 3.4 (3.3-3.6); for photographs of skull, seePlate 1e, andPlate 3e.

Comparisons.—For comparisons withB. m. brunneus,B. m. infernatis, andB. m. pallidus, see accounts of those subspecies. FromB. m. nigrescens,B. m. musculusdiffers in: dorsum paler throughout (less of blackish brown); region of face and ears paler, more buff and fawn-colored hairs rather than blackish-brown to grayish hairs; vibrissae paler; venter paler, less dark gray and less of sooty-colored undertones, tips of hairs whitish to pale Olive-Buff rather than light gray at tips becoming darker basally; forefeet and hind feet paler, whitish to pale buff-color with flesh-colored undertones, not sooty-colored to dark brown; tail paler below; nasals flaring outward, not tapering toward midline at anteriormost point; zygoma more massive; larger in external and cranial dimensions.

Remarks.—Merriam (1892:170) describedSitomys[=Baiomys]musculuson the basis of 23 specimens (from Colima City, Colima; Armeria, Colima; Plantinar, and Zapotlán, Jalisco). According to the original description,B. musculusresembled a small house mouse and was smaller than any known species ofSitomysexceptS. taylori[=Baiomys taylori]. Fromtaylori,musculusdiffered in being larger [in size of body], and in having longer ears and tail, and larger hind feet. When Allen and Chapman (1897:203) describedPeromyscus[=Baiomys]musculus brunneusfrom Jalapa, Veracruz, the specimens described by Merriam from Colima and Jalisco became representative of the nominal subspeciesB. m. musculus. Osgood (1909:258) assigned specimens from Colima, Guerrero, Jalisco, Michoacán, Morelos, Oaxaca, Puebla, Sinaloa, Veracruz, and Zacatecas to the subspeciesmusculus. Subsequently, Russell (1952:21) named the subspeciespallidusfrom the arid lowlands of Morelos; Hooper (1952:96) described the subspeciesinfernatisfrom northern Oaxaca and southeastern Puebla; and Goodwin (1959:1) described a new subspeciesnebulosusfrom the Oaxaca highlands. Each of the subspecies mentioned immediately above was described from within the geographic range assigned toB. m. musculusby Osgood (loc. cit.). Hall and Kelson (1959:661) mapped the range ofB. m. musculusso as to include Colima, parts of Jalisco, Michoacán, Guerrero, Oaxaca, and Veracruz. Lukens (1955:159), in a study of the mammals of Guerrero, has shown that the characters attributed toB. m. pallidusare not significantly different from those of pygmy mice studied from Guerrero. He (loc. cit.) concluded that: (1) if the specimens of pygmy mice from central Guerrero were typical of the subspeciesmusculus, thenpallidusdid not deserve subspecific recognition, or; (2) the nameB. m. musculusshould be restricted to the larger pygmy mice inhabiting the lowlands immediately adjacent to the Pacific Coast and the area to the north. My data (seeFigure 12) show pygmy mice from southwestern Nayarit, northwestern and central Jalisco, Colima, and parts of Michoacán to be significantly larger in certain cranial and external measurements than pygmy mice from Guerrero, Oaxaca, Morelos, and parts of Puebla. This finding essentially corroborates Hooper's (1952a:96) findings. It seems advisable, therefore, to restrict the range ofB. musculus musculusto the large mice inhabiting west-central México and the coastal lowlands of Colima and Michoacán. The namepallidusis applicable to the smaller mice occupying Morelos, southwestern Puebla, Guerrero, Oaxaca, and southwestern Chiapas.

B. m. musculusintergrades withB. m. pallidusin eastern Michoacán and central and western Guerrero. Specimens from San José Prura and 12 mi. S Tzitzio, Michoacán, though referable toB. m. musculusbecause of slightly larger size of crania are intermediate in size and color between the smaller and slightly darkerpallidusto the south and east and the larger, slightly palermusculusto the northwest.

Specimens examined.—Total 156 all from the Republic of México, and distributed as follows:Nayarit: 3 mi. NNW Las Varas, 150 ft., 1.Jalisco: 7 mi. W Ameca, 4000 ft., 2[10];6 mi. W Ameca, 4300 ft., 3[10];10 mi. S Ameca, 5800 ft., 1[10];13 mi. S, 15 mi. W Guadalajara, 3;13 mi. S, 91/2mi. W Guadalajara, 1;3 mi. ENE Santa Cruz de las Flores, 1; 27 mi. S, 12 mi. W Guadalajara, 1;4 mi. NE Autlán, 3000 ft., 5[10];Sierra de Autlán, 5000 ft., 2[10];21/2mi. NNE Autlán, 3000 ft., 8; 2 mi. SSE Autlán, 1;5 mi. S Purificación, 2; Chamela Bay, 1[10];2 mi. N La Resolana, 1500 ft., 6[10];1 mi. N San Gabriel, 4000 ft., 32[10]; 2 mi. N Cuidad Guzmán, 5000 ft., 1; 3 mi. E Navidad, 4300 ft., 10[10].Colima:type locality, 10[11](including the type);3 mi. SE Colima(City), 5[10];4 mi. SW Colima City, 1; Armeria, 200 ft., 8[11];Paso del Río, 20[10].[Pg 623]Michoacán: 12 mi. S Tzitzio, 6[10]; San José Prura, 4[12]; 1 mi. E, 6 mi. S Tacámbaro, 4000 ft., 3[13]; La Salada, 3[11];1/2mi. SE Coalcomán, 15[10].Marginal records.—Nayarit: 3 mi. NNW Las Varas, 150 ft.Jalisco: 3 mi. E Navidad, 4300 ft.; 27 mi. S, 12 mi. W Guadalajara.Michoacán: 12 mi. S Tzitzio; San José Prura;1/2mi. SE Coalcomán.Colima: Armeria, 200 ft.Jalisco: Chamela Bay.

Marginal records.—Nayarit: 3 mi. NNW Las Varas, 150 ft.Jalisco: 3 mi. E Navidad, 4300 ft.; 27 mi. S, 12 mi. W Guadalajara.Michoacán: 12 mi. S Tzitzio; San José Prura;1/2mi. SE Coalcomán.Colima: Armeria, 200 ft.Jalisco: Chamela Bay.

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