Chapter 6

Fig. 11.Distribution ofBaiomys taylori. 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. t. allex2.B. t. analogous3.B. t. ater4.B. t. canutus5.B. t. fuliginatus6.B. t. paulus7.B. t. subater8.B. t. tayloriNatural HistoryHabitat and numbers.—The habitat occupied by the northern pygmy mouse ranges from sparse grassy areas along rock walls in central México (see Davis, 1944:394), and mesquite-cactus associations in southern Texas (Blair, 1952:242) to heavy stands of grasses such asBoutelouasp.,Andropogonsp.,Hilariasp., and sacaton grass intermixed withYucca glaucain New Mexico, Arizona (see Hoffmeister 1956:281), and Chihuahua. Baker (1951:213) reports the species from 2 km. W El Carrizo, Tamaulipas, in dense grass and weeds at the edge of a cornfield. Hooper (1953:7) recorded the northern pygmy mouse in a cultivated field overgrown with herbaceous vegetation at Pano Ayuctle, Tamaulipas. In the State of Sinaloa, Hooper (1955b:13) obtained specimens in grass and among shrubs and vines bordering a fallow field. The northern pygmy mouse, in general, lives in situations more xerophytic and more grassy than does the southern pygmy mouse.The northern pygmy mouse, as the southern pygmy mouse, is locally abundant in its geographic range. Stickel and Stickel (op. cit.: 145) pointed out that on the third night of live-trapping in Bexar County, Texas, there was a sudden increase in unmarked pygmy mice trapped. This increase in numbers, after the resident population was seemingly marked, followed a one-half inch rainfall. Collectors from the University of Kansas, myself included, have had similar experiences in trapping these mice. In the Mexican states of Guanajuato, Querétaro, and Jalisco,B. tayloriis one of the commonest small mammals. In New Mexico and Arizona and the Mexican states of Sonora and Sinaloa, nevertheless, these mice are rare.Stickel and Stickel (loc. cit.) thought that the home range normal forB. tayloriin a grassy habitat was less than 100 square feet, but Blair (1953:10) thought that a complete home range had not been recorded by Stickel and Stickel.Behavior.—The northern pygmy mouse is crepuscular to nocturnal and where I trapped in northern Mexico was one of the first small rodents to appear in my traps in the evening. Hall and Villa-R (1949:460) recorded this habit in Michoacán. Observations of wild-takenB. tayloriheld in captivity, lend support to its being crepuscular. Captives were rarely active in bright lights, but in diffuse or dim lights the same mice were active.Blair (1941:381) pointed out that captiveB. t. subaterwere much more tolerant of one another than mice of the genusPeromyscus. He pointed out also that males aided in care of young. In onelitter born in captivity in the course of my study, the female killed the male when the young were four days old. In another instance, the female and two eight-day-old young were killed by the male. Until that time, the male, female, and young had lived together peacefully. In other litters born in captivity, adult males did not harm the other mice.I have noted, as Blair (loc. cit.) did, thatB. tayloriutters high-pitched squeals in a "singing" posture resembling that of the coyote, yet remains silent when being handled.The northern pygmy mouse makes runways in the grass, in miniature resembling those ofMicrotus, and often uses runways constructed bySigmodon. A small firm nest of finely shredded plant material (mostly grasses) is constructed in burrows or under logs, rocks, or fallen cactus plants. Thomas (1888:447) recorded nests of fine curly grass and cornsilk. Secondary refuge nests are not uncommon. Thomas (loc. cit.) states, "If other mice live in the same place, the individuals ofBaiomyswatch till others disappear, then suddenly steal part of the other nest and run to their own with it."Enemies and food.—Little is recorded of the animals that prey upon the northern pygmy mouse. Twente and Baker (1951:120) found remains ofB. tayloriin 16 per cent of barn owl pellets (Tyto alba pratincola) collected 21 mi. SW Guadalajara, Jalisco. Presumably most of the crepuscular and early nocturnal raptorial birds and carnivorous mammals feed on these mice.Food ofB. tayloriconsists in part of grass seeds and leaves, prickly pear (Opuntiasp.) and the softer exposed parts of roots of vegetation among which the mice reside.Reproduction.—The northern pygmy mouse breeds throughout the year. The only months in which I have not recorded pregnant females or females with young are June and October. Forty-one records of embryos or young per litter average 2.48 (less than inB. musculus), and range from as few as one to as many as four per litter.Baiomys taylori allex(Osgood)Peromyscus allexOsgood, Proc. Biol. Soc. Washington, 17:76-77, March 21, 1904; Elliot, Field Columb. Mus. Publ., 105(6):135, July 1, 1905; Lyon and Osgood, Bull. U. S. Nat. Mus., 62:124, January 15, 1909.Baiomys taylori allex, Packard, Proc. Biol. Soc. Washington, 71:17, April 11, 1958; Hall and Kelson, The Mammals of North America, 2:659, March 31, 1959 (part).[Peromyscus]allex, Elliot, Field Columb. Mus. Publ., 95(4):175, July 15, 1904.Peromyscus taylori paulus, Osgood, N. Amer. Fauna, 28:255, April 17, 1909 (part).Baiomys taylori paulus, Miller, Bull. U. S. Nat. Mus., 79:137, December 31, 1912 (part); Miller, Bull. U. S. Nat. Mus., 128:317, April 29, 1924 (part); Ellerman, The Families and Genera of Living Rodents, British Mus. Nat. Hist., 2:402, March 21, 1941 (part); Poole and Schantz, Bull. U. S. Nat. Mus., 178:259, March 6, 1942; Goldman, Smith. Miscl. Coll., 115:373, July 31, 1951 (part); Miller and Kellogg, Bull. U. S. Nat. Mus., 205:512, March 3, 1955 (part); Hall and Kelson, The Mammals of North America, 2:659, March 31, 1959 (part).Baiomys taylori analogous, Hall and Kelson, Univ. Kansas Publs., Mus. Nat. Hist., 5:367, December 15, 1952 (part).Type.—Adult male, skin and skull; No. 33429/45452 U. S. Nat. Mus. (Biol. Surv. Coll.); Colima (City), Colima, Republic of México, obtained on March 7, 1892, by E. W. Nelson, original number 2029.Range.—Colima, western lowlands of Michoacán and Jalisco, thence north into southern half of Nayarit, seeFigure 11. Zonal range: arid lower tropical, approximates northern half of the Nayarit-Guerrero Biotic Province of Goldman and Moore (1945:349). Occurs from near sea level in Nayarit, up to 4000 feet in Jalisco.Diagnosis.—Size small for the species; dorsal ground color pale grayish-brown, near Isabella color; mid-dorsal region washed with blackish, individual guard hairs black to base, other hairs black-tipped with subterminal light olive bands, Neutral Gray at base; laterally, black-tipped hairs less abundant, hairs grayish-white to base; venter Pale Gull Gray to whitish, distal half of individual hairs white, proximal half Neutral Gray; hairs in regions of throat and chin white to base; facial region colored like dorsum, becoming paler below eye; in region of mouth, hairs white to base; dorsalmost vibrissae black to base, others white to base; ears flesh-colored, sparsely haired; tail unicolored, sparsely haired for the species; dark blotches on tail of some series (particularly the paratypical series); dorsal and ventral parts of forefeet and hind feet flesh-colored, whitish to gray in some series. Slightly smaller in most cranial dimensions. Maxillary part of zygoma forming almost a right angle with rostrum, rather than tapering at less than a right angle to rostrum; supraoccipital rounded posteriorly rather than indented on each side of foramen magnum; cranium, relative to length of rostrum, more nearly square; interparietal large relative to size of cranium. Average and extreme measurements of five adults from 2 mi. SSE Autlán are as follows: total length, 100.0 (93-107); length of tail vertebrae, 40.0 (37-44); length of body, 60.0 (56-63); length of hind foot, 14.0 (14); length of ear from notch, 10.5 (10-11); occipitonasal length, 17.3 (16.8-17.9); zygomatic breadth, 9.1 (8.7-9.4); postpalatal length, 6.3 (6.0-6.6); least interorbital breadth, 3.4 (3.3-3.5); length of incisive foramina, 3.9 (3.8-4.0); length of rostrum, 5.5 (5.2-5.8); breadth of braincase, 8.6 (8.0-8.9); depth of cranium, 6.4 (6.0-6.7); alveolar length of maxillary tooth-row, 3.0 (2.8-3.1); for photographs of skull, seePlate 1iandPlate 4a.Comparisons.—For comparisons withB. t. canutus, see account of that subspecies. FromB. t. analogous,B. t. allexdiffers in: external and cranial dimensions less; dorsal coloration paler; tail and ears paler and less hairy; dorsum and belly paler; dorsal and ventral parts of forefeet and hind feet paler; median parts of incisive foramina less constricted on either side of midline and wider open laterally; interparietal larger in relation to skull; interorbital breadth greater relative to occipitonasal length.[Pg 635]B. t. allexdiffers fromB. t. paulusas follows: dorsum gray with yellowish-brown wash rather than fawn to buff; tail unicolored in most series, less hairy; hind feet flesh-colored to light sooty, rather than whitish; rostrum slightly longer relative to occipitonasal length; incisive foramina differ from those ofpaulusin much the same way as fromanalogous.Remarks.—Osgood (1909:255-256) dismissed as taxonomically unimportant the differences in color of pelage and size of cranium that he observed between the specimens from Colima (City), Colima, representative ofallexand those representingpaulusand chose to synonomizeallexwithpaulus. The differences that Osgood (loc. cit.) deemed "… scarcely worthy of recognition …," are, in fact, not only worthy of recognition, but also important in an understanding of the evolution ofBaiomys taylori(see speciationp. 659). Recently, I (1958b:17-18) studied ten specimens from Colima (City), Colima, and chose to regardPeromyscus [= Baiomys] allexas a subspecies. I suggested (loc. cit.) that the geographic range ofB. t. allexmight encompass the southern part of Nayarit, and western Jalisco. Subsequent study of specimens from these areas reveals that the populations there are referable toallex. Most of the specimens obtained from these areas, however, merit special comment.In color of pelage, those populations from south of the Río Grande de Santiago and northwest of Guadalajara (4 mi. SE Ahuacatlán; 1 mi. E Ixtlán; Etzatlán) show evidence of intergradation withpaulusto the east and south (Magdalena, Tequila, and Tala, Jalisco), and with populations more closely adjacent to the south bank of that river. Intergradation is indeed complex in this area. Specimens from some localities seem to be intergrades betweenallexandpaulus; from other localities, some specimens are referable toallex, and the others topaulus; from still other localities, all specimens are referable toallex.A series of 39 specimens from 1 mi. SSE Ameca, 4000 ft., Jalisco, are uniformly grayish-brown. This series averages grayer than paratypes ofallex. There is little, if any, difference between the series from 1 mi. SSE Ameca and paratypes ofallexin external size of body, hind foot, length of ear, and size and conformation of the cranium. Populations from Ameca and vicinity might be expected to average considerably larger inasmuch as they occur at higher altitudes (see Bergman's Rule,p. 609) then the material from the lower coastal plains to the south in Colima and Michoacán, and at lower elevations in the west in Jalisco and Nayarit. The means of externaland cranial measurements are not significantly different between the specimens from the highlands and those from the lowlands. In the area of Ameca where the two speciesB. musculusandB. taylorioccur together, interspecific competition seems to have limited, perhaps even reduced, size of external and cranial parts oftaylori(seep. 660).In color, specimens from the northern part of the valley of the Río Tepalcatepec (10 mi. S, 1 mi. W Apatzingán) in Michoacán resemble paratypes ofallex. Intergradation probably occurs to the north withanalogous.In the eight specimens from 13 mi. E and 1 mi. N Talpa de Allendé, the skull, as reflected in occipitonasal length and zygomatic breadth relative to length of body, is larger than in other specimens here assigned toallex. The median part of the belly of the eight specimens is buff-colored rather than whitish-gray as in typicalallex; the mid-dorsal region also averages darker than in any other specimens referred toallex. Additional specimens are needed from this and closely adjacent areas, especially to the west on the coastal plain, in order to determine more accurately the taxonomic status of the mice there. At present, it seems best to refer them toallex. Possibly the population represented by the eight specimens is an incipient subspecies.There is no evidence of hybridization or intergradation of populations ofB. t. allexwith any population ofB. musculuswhere the two species occur together.Specimens examined.—Total 233, all from the Republic of México, distributed as follows:Nayarit: 3 mi. SE Mirador, 7; 2mi. S. Compostela, 2900 ft., 5; 4mi. N Santa Isabel, 3800 ft., 2[25];2 mi. N Santa Isabel, 3800 ft., 22[25];4 mi SE Ahuacatlán, 5200 ft., 2[26];1 mi. E Ixtlán, 4000 ft., 13[25]; 1 mi. E Ixtlán del Río, 3700 ft., 1; 2 mi. WNW Valle de Banderas, near sea level, 1.Jalisco: Arroyo de Gavalán, 16[28]; Etzatlán, 6[27];Mascota, 3900 ft., 6[27];7 mi W Ameca, 15[25];6 mi. W Ameca, 15[25];3 mi. W Ameca, 5[25]; Ameca, 4000 ft., 11[27];1 mi. SSE Ameca, 4000 ft., 38; 2 mi. N Resolana, 1500 ft., 28[25]; 13 mi. E, 1 mi. N Talpa de Allendé, 8; 2 mi. SSE Autlán, 5; 1 mi. N San Gabriel, 4000 ft., 1[25]; Las Canoas, l[28].Colima: Type locality, 10[27](including the type).Michoacán: 9 mi. S Lombardia, 1500 ft., 1;3 mi. W Apatzingán, 1000 ft, 1; Apatzingán, 3[25]; 10 mi. S, 1 mi. W Apatzingán, 800 ft., 10.Marginal records.—Nayarit: 3 mi. SE Mirador; 1 mi. E Ixtlán del Río.Jalisco: Etzatlán; Ameca; 2 mi. N Resolana; Las Canoas.Michoacán: 9 mi. S Lombardia; 10 mi. S, 1 mi. W Apatzingán.Colima: type locality.Nayarit: Valle de Banderas.[25]Univ. Michigan, Museum of Zoology.[26]California Academy of Sciences.[27]U. S. Nat. Museum (Biol. Surv. Coll.).[28]American Museum of Natural History.Baiomys taylori analogous(Osgood)Peromyscus taylori analogousOsgood, N. Amer. Fauna, 28:256, April 17, 1909 (part); Elliott, Check-List Mamm., N. Amer. Cont., West Indies and Neighboring Seas, Suppl., Amer. Mus. Nat. Hist., p. 44, January 8, 1917.Baiomys taylori analogous, 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, British Mus. Nat. Hist., 2:402, March 21, 1941; Poole and Schantz, Bull. U. S. Nat. Mus., 178:259, March 6, 1942; Davis, Jour. Mamm., 25:394, December 12, 1944; Hooper, Jour. Mamm., 28:50, February 15, 1947; Hall and Villa-R., Univ. Kansas Publs., Mus. Nat. Hist., 1:460, December 27, 1949; Hall and Villa-R., Anal. del Inst. Biol., 21:196, September 28, 1950; Goldman, Smith. Miscl. Coll., 114:373, July 31, 1951 (part); Hall and Kelson, Univ. Kansas Publs., Mus. Nat. Hist., 5:367, December 15, 1952 (part); Villa-R., Anal. del Inst. Biol., 23:435, May 20, 1953; Miller and Kellogg, Bull. U. S. Nat. Mus., 205:512, March 3, 1955; Hooper, Occas. Papers Mus. Zool. Univ. Michigan, 565:13, March 31, 1955; Packard, Proc. Biol. Soc. Washington, 71:17, April 11, 1958.Peromyscus musculus brunneus, Elliot, Field Columb. Mus. Publ., 115(8):203, 1907 (part).Peromyscus musculus[musculus], Osgood, N. Amer. Fauna, 28:258, April 17, 1909 (part).Baiomys musculus musculus, 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).Baiomys taylori taylori, Dalquest, Louisiana State Univ. Studies (Biol. Sci. Ser.), 1:155, December 28, 1953 (part); Hall and Kelson, The Mammals of North America, 2:660, March 31, 1959 (part).Baiomys taylori allex, Hall and Kelson, The Mammals of North America, 2:659, March 31, 1959 (part).Baiomys musculus musculus, Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part).Type.—Adult male, skin and skull; No. 120261 U. S. Nat. Mus. (Biol. Surv. Coll.); Zamora, Michoacán, Republic of México, obtained on January 15, 1903, by E. W. Nelson, and E. A. Goldman, original number 15764.Range.—Central and eastern Jalisco south into Michoacán, east through Guanajuato, Querétaro, thence into Estado México, and Distrito Federal, and west-central Veracruz, seeFigure 11. Zonal range: approximately the Transverse Volcanic Biotic Province of Moore (1945:218) and of Goldman and Moore (1945:349). Occurs from 5000 feet, 7 mi. S Ocotlán, Jalisco, up to 8000 feet in Ixtapalapa, Distrito Federal.Diagnosis.—Size large for the species; dorsum dark Sepia to near blackish medially in freshly taken specimens (Sepia fading to near Fuscous in prepared specimens); belly slaty-gray, hairs Deep Neutral Gray near tips and Dusky Neutral Gray at bases; hairs on back black-tipped with subterminal band of Ochraceous-Tawny (guard hairs blackish to base); hairs of throat and chin white-tipped, gray at bases; dorsal vibrissae black, ventral and anteriormost vibrissae white; hairs on face and sides black-tipped, and Ochraceous-Tawny at base; ears sparsely haired, individual hairs grayish, blackish, and ochraceous;[Pg 638]tail sooty to blackish dorsally, lighter ventrally; forefeet and hind feet sooty brown on dorsal and ventral surface. Skull relatively broad interorbitally; zygoma broad and squared; cranium larger in all dimensions than in most other subspecies. Average and extreme measurements of 10 adults from 1 mi. S, 11 mi. W Zamora, 5400 ft., Michoacán, are: total length, 109.4 (102-121); length of body, 64.3 (58-72); length of tail, 44.9 (39-51); length of hind foot, 14.6 (14-15); occipitonasal length, 18.0 (17.5-18.6); zygomatic breadth, 9.4 (9.1-9.7); postpalatal length, 6.6 (6.2-7.2); least interorbital breadth, 3.5 (3.3-3.8); length of incisive foramina, 4.0 (3.8-4.2); length of rostrum, 6.2 (5.8-6.5); breadth of braincase, 8.7 (8.5-8.9); depth of cranium, 6.6 (6.3-6.9); alveolar length of maxillary tooth-row, 3.1 (3.0-3.3); for photographs of skull, seePlate 2aandPlate 4b.Comparisons.—For comparisons withB. t. allex,B. t. canutus,B. t. paulus, andB. t. fuliginatus, see accounts of those subspecies. FromB. t. taylori,B. t. analogousdiffers as follows: sides and dorsum darker, differing most in freshly prepared specimens; dorsal surface of forefeet and hind feet darker; basal part of hairs on belly darker gray; frontal bones less constricted, causing less taper anteriorly in interorbital space; interparietal wider transversely; basioccipital more expanded laterally, narrowing more abruptly at suture between basioccipital and basisphenoid.Remarks.—The pelage ofanalogousbecomes paler with wear as pointed out by Osgood (1909:257). A paratype, U. S. Nat. Mus. 120260, and several specimens from 1 mi. S, 11 mi. W Zamora, Michoacán, are grayish rather than brownish-black. All of these are old adults having the terminal black parts of the hairs on the dorsum nearly worn away. Excluding such grayish individuals,B. t. analogous, likeB. t. subaterandB. t. fuliginatus, is uniformly brownish-black. Bothanalogousandfuliginatusoccur in relatively high mountainous country on dark soils or pedregals, and all three of the aforementioned subspecies occur in zones of high relative humidity.B. t. analogousintergrades withB. t. paulus(see account of that subspecies) andB. t. allexsouth and west of Lago de Chapala in Jalisco. Additional specimens are needed from Querétaro and San Luis Potosí in order to ascertain whether or notB. t. analogousintergrades withB. t. fuliginatusorB. t. taylori. Specimens from western Jalisco, in the past referred toB. t. analogous, are referable toB. t. allex(see account of that subspecies). Specimens obtained west of, and bordering, the Río del Naranjo in Jalisco show a mixture of characters of bothB. t. allexandB. t. analogous. For example, specimens from 2 mi. N Ciudad Guzmán resembleanalogouson the dorsum, whereas, on the belly, the individual hairs are white-tipped, pale gray at the base, and in over-all appearance are whitish-gray, unlike typicalanalogous(being likeallexinstead). The dorsal surface of the forefeet are sooty to light brownish (as inanalogous),whereas, the hind feet are flesh-colored (as inallex). Another series of specimens from 4 mi. W León, Guanajuato, are intergrades betweenB. t. analogousandB. t. paulus. These specimens are grayish to brownish on the dorsum, have sooty forefeet and hind feet (more nearly as inanalogousthan inpaulus), are grayish-white on the venter, and have a distinctly bicolored tail (resembling that ofpaulusmore than that ofanalogous). When the average of cranial characters is considered, both series are best referred toanalogous.Hooper (1947:50) pointed out that specimens from the pedregal San Gerónimo, Distrito Federal, were more nearly black than topotypes and generally showed less brownish hues typical ofanalogous. I have examined this series and several others from this area (see Specimens examined,p. 640) and am convinced that these populations average darker. Actually, the dorsum is more nearly black and the venter is more buffy than in typicalanalogous. The hairs of these individuals average longer than in other populations ofanalogous. Skulls of the specimens from the pedregal are indistinguishable from those of paratypes ofanalogous. The populations from the Distrito Federal seem to be incipient subspecies.Specimens examined.—Total 696, all from the Republic of México, distributed as follows:San Luis Potosí: Hacienda Capulín, 5[33];3.3 mi. N Tamazunchale, by-road, 2[34]; 1 mi. N Tamazunchale, 700 ft., 1[35].Veracruz: Acultzingo, 4[29], 1[31].Jalisco: 1 mi. S Jalostotitlán, 5700 ft., 5; 7 mi. NW Tepatitlán, 3[29];6 mi. N, 4 mi. E Tepatitlán, 6400 ft., 25;21/2mi. E Tepatitlán, 6200 ft., 15;2 mi. S,1/2mi. W Tepatitlán, 9;near Tepatitlán, 2;5 mi. SW Arrandas, 6700 ft., 6;2 mi. E Zapotlanejo, 23;21/2mi. E Puente Grande(51/2mi. SW Zapotlanejo), 3;8 mi. S Guadalajara, 10[29];3 mi. ENE Santa Cruz de las Flores, 9;4 mi. NE Ocotlán, 5050 ft., 18;13 mi. S, 91/2mi. W Guadalajara, 1;2 mi. WNW Ocotlán, 5000 ft., 15; 13 mi. S, 15 mi. W Guadalajara, 2;Ocotlán, 5000 ft., 8[30];1 mi. S Ocotlán, 5000 ft., 12; 27 mi. S, 12 mi. W Guadalajara, 9;11/2mi. N Mazatmitla, 6[29];1/2mi. NW Mazatmitla, 4;3 mi. WSW Mazatmitla, 4; 2 mi. N Ciudad Guzmán, 5000 ft., 18.Guanajuato: 4 mi. N, 5 mi. W León, 7000 ft., 25; 5 mi. S Salamanca, 2[29];5 mi. E Celaya, 6000 ft., 6;1 mi. E Yuriria, 5725 ft., 3; Salvatierra, 5775 ft., 8;NE edge Acambaro, 6050 ft., 10;Acambaro, 3[30].Querétaro: Tolimán, 7[30]; 6 mi. E Querétaro, 6550 ft., 37.Hidalgo: Tula, 2050 m., 1[31].Michoacán:2 mi. E La Palma, SE side Lago de Chapala, 7; type locality, 4000 ft., 10[30](including the type);9 mi. E Zamora(Camenaro), 2[29];1 mi. S, 11 mi. W Zamora, 5400 ft., 17; S Cuitzeo, 36[29];Jiquilpan, 4800 ft., 15;11 mi. W Jiquilpan, 6700 ft., 2;1 mi. E Jiquilpan, 7;1 mi. E Zinapecuaro, 6300 ft., 17;41/2mi. NE Tarequato(Tarecuato), 6600 ft, 1;Tanganciguaro(Tangancicuaro), 5500 ft., 4;2 mi. N Tarecuato, 7200 ft., 1;2 mi. S Maravatio, 6650 ft, 6;2 mi. SE Zacapu, 6600 ft., 11;1 mi. N Tinquindin(Tinguindin), 6300 ft., 2;3 mi. E Morelia, 6600 ft., 3;11 mi. E, 2 mi. S Morelia, 1; 2 mi. SE Hidalgo (Villa Hidalgo), 6;11/2mi. N Los Reyes, 1;E Los Reyes, 18[29];Los Reyes, 8[30];3 mi. W, 1 mi. N Pátzucuaro, 6600 ft., 2;N Pátzucuaro, 2[29];Pátzucuaro9[31], 4[30], 4[29]; Uruapan, 1[29];E Uruapan, 12;21/2mi. E Uruapan(La Presca), 2[29]; 2 mi. SW Zitacuaro, 1; 1 mi. E, 6 mi. S Tacámbaro, 4000 ft., 11[37];La Huacana, 1[30].Mexico: Templo del Sol, Pyramídes de San Juan,[Pg 640]Teotihuacán, 8000 ft., 1;31 km. E México City, 7500 ft., 11[36];17 km. E México City, 7500 ft, 1[36];Cerro La Caldera, 11 mi. ESE México, 2350 m., 5; 4 km. ENE Tlalmanalco, 2290 m., 9;Hacienda Córdoba(Córdova), 6.Mexico, D. F.:Cerro de la Estrella, Ixtapalapa, 2450 m., 1;3/4mi. S, 1 mi. E Churubusco, 2400 m., 2;5 km. S México City, South of Cd. Universitaria, l[32];Pedregal San Angel,2.6 mi. S Monumento a Obregón, 2;El Pedregal, 1 km. S San Angel, 2260 m., 1;Falda SW Cerro Zacatepec, 3.9 mi. SW Monumento a Obregón, 1;2 mi. N Tlalpan, Zacayuca, 2380 m., 5;Tlalpan(Pedregal), 2400 m., 21[31];San Gerónimo, 37[29], 6[38];Santa Rosa, 2700 m., 1[32];Tlalpan, 8;3/4mi. SW Las Fuentes, Tlalpan, 2450 m., 25[30];Tepepán, 6[29];Rancho La Noria, 1 mi. W Xochimilco, 2270 m., 4;500 meters N Xochitepec, 2250 m., 7; 200 m. N San Mateo Xalpa (Jalpa), 2390 m., 2.Marginal records.—San Luis Potosí: Hacienda Capulín; 1 mi. N Tamazunchale.Hidalgo: Tula, 2050 m.Mexico: Templo del Sol, Pyramídes de San Juan, Teotihuacán.Veracruz: Acultzingo.Mexico: 4 km. ENE Tlalmanalco.Mexico, D. F.: 200 m. N San Mateo Xalpa (Jalpa), 2390 m.Michoacán: 2 mi. SW Zitacuaro; 1 mi. E, 6 mi. S Tacámbaro; Uruapan.Jalisco: 2 mi. N Ciudad Guzmán; 27 mi. S, 12 mi. W Guadalajara; 13 mi. S, 15 mi. W Guadalajara; 7 mi. NW Tepatitlán; 1 mi. S Jalostotitlán, 5700 ft.Guanajuato: 4 mi. N, 5 mi. W León.Querétaro: 6 mi. E Querétaro, 6550 ft.; Tolimán.[29]Univ. Michigan, Museum of Zoology.[30]U. S. Nat. Museum (Biol. Surv. Coll.).[31]Chicago Natural History Museum.[32]American Museum of Natural History.[33]Museum of Natural History, Louisiana State University.[34]Univ. Illinois, Mus. Nat. History.[35]The Museum, Michigan State Univ.[36]Texas A & M, Cooperative Wildlife Research Collection.[37]Univ. California, Mus. Vert. Zoology.[38]University of Florida Collections.Baiomys taylori ater(Blossom and Burt)Baiomys taylori aterBlossom and Burt, Occas. Papers Mus. Zool., Univ. Michigan, 465:2, October 8, 1942; Blair and Blossom, Contrib. Lab. Vert. Biol., Univ. Michigan, 40:1, March, 1948; Hoffmeister and Goodpaster, Ill. Biol. Monogr., 24(1):115, December 31, 1954; Miller and Kellogg, Bull. U. S. Nat. Mus., 205:511, March 3, 1955; Hoffmeister, Amer. Midland Nat., 55:281, April, 1956; Packard, Jour. Mamm., 40:146, February 20, 1959; Hall and Kelson, The Mammals of North America, 2:659, March 31, 1959 (part).Peromyscus taylori paulus, Osgood, N. Amer. Fauna, 28:256, April 17, 1909 (part).Baiomys taylori[ater], Justice, Jour. Mamm., 38:520, November 20, 1957.Type.—Adult male, skin and skull; No. 85425, University of Michigan, Museum of Zoology; 7 mi. W Hereford, Cochise County, Arizona, obtained on March 25, 1941, by Philip M. Blossom, original number 2195.Range.—Southeastern Arizona, north to Graham County, thence east to the Animas Valley, Hidalgo County, New Mexico; south to northern Chihuahua and northwest to the southern border of Cochise County, Arizona, seeFigure 11. Zonal range: largely lower Sonoran (Apachian Biotic Province of Dice, 1943:56). Occurs from 4300 feet in Chihuahua up to 6200 feet in New Mexico.Diagnosis.—Size medium for the species; dorsum between Mummy Brown and Prouts Brown; individual tips of hairs intermixture of black and Ochraceous-Tawny, bases of all hairs slate-gray; sides of body and face, Buffy Brown to Cinnamon Brown; belly Cinnamon Buff, proximal half of individual hairs Deep Neutral Gray, distal half white; in region of throat, proximal[Pg 641]fourth of individual hairs gray, distal three-fourths white; dorsal vibrissae black to base, ventral vibrissae white to base; tail brownish above, gray below; dorsal and ventral surface of forefeet and hind feet buffy to gray; interparietal somewhat compressed anteroposteriorly. Average and extreme cranial measurements of 15 adults from 91/2mi. W New Mexico State Line, 51/2mi. N Mexican border, Cochise County, Arizona, are as follows: occipitonasal length, 18.0 (17.5-18.6); zygomatic breadth, 9.5 (9.2-9.9); postpalatal length, 6.6 (6.0-7.1); least interorbital breadth, 3.6 (3.4-3.8); length of incisive foramina, 4.0 (3.8-4.2); length of rostrum, 6.1 (5.7-6.4); breadth of braincase, 8.6 (8.4-9.1); depth of cranium, 6.5 (6.3-6.9); alveolar length of maxillary tooth-row, 3.2 (3.1-3.4). Average and extreme external measurements for six adults from 9 mi. W Hereford, Cochise County, are as follows: total length, 106.3 (98-115); length of tail vertebrae, 42.3 (39-46); length of body, 64 (59-69); length of hind foot, 13.6 (13-14.2); length of ear from notch, 11.1 (10.5-11.5); for photographs of skull, seePlate 2b, andPlate 4c.Comparisons.—For comparisons withB. t. canutus, see account of that subspecies. FromB. t. paulus, the subspecies to the southeast,B. t. aterdiffers in: dorsum darker brown; tail less strikingly bicolored; belly buffy rather than whitish to white-gray; forefeet and hind feet darker dorsally and ventrally; posterior margin of basioccipital bowed anteriorly in a broad U-shape with a secondary small median anteriorly directed U-shaped curve, rather than bowed anteriorly in a simple U-shape; interparietal more compressed anteroposteriorly; coronoid process of mandible so acutely recurved that tip of coronoid points posteroventrally and appears sickle-shaped.Remarks.—Blossom and Burt (1942:1) describedB. t. ateras the darkest of the known subspecies. It is dark, but specimens from some parts of the ranges ofB. t. analogous,B. t. fuliginatus, andB. t. subaterexceed in melanins the darkest individuals ofater. Blair and Blossom (1948:5) also concluded by the use of an Ives tint photometer thatB. t. subaterwas significantly darker thanB. t. ater.When paratypes ofaterand specimens ofB. t. paulusare compared, the darkest individuals ofaterexceed but slightly the darkest ofpaulus. The darkest specimens ofpaulusoccur in southern Zacatecas, and northern Jalisco, and the palest of the series are in northern Durango and southern Chihuahua. When paratypes ofaterandpaulusare compared, the difference in color is readily distinguishable. Specimens from 11/2mi. N San Francisco, in northern Chihuahua, appear to be intermediate in color betweenaterandpaulusexcept for a faint tinge of buff ventrally. In characters of the crania, these specimens resembleaterand are referred to that subspecies. A slightly different pattern of color is present in pygmy mice from the Peloncillo Mountains and the Animas Valley of New Mexico; the upper parts resemble those of paratypes ofater, but the venter has only the faintest suggestion of thebuffy wash. Crania of these specimens from New Mexico are inseparable from those of paratypes ofater, and the specimens are, therefore, referred toater.When specimens are arranged by localities from Arizona east into southern New Mexico, thence south into Chihuahua and Durango, gradual intergradation in color is evident from dark in the north to pale browns in the south, whereas, size and shape of interparietal and size and shape of coronoid process of the lower jaw divide quite distinctly into two morphological types in central Chihuahua.Cranial variation in size and proportion among adults is slight throughout the range ofatercompared to variation detected in other subspecies ofBaiomys taylori. Perhaps such a relatively stable pattern of characters of the crania reflects the homogeneity of the gene pool, with respect to these characters, of the populations sampled. The fact that the color of the pelage of this subspecies varies considerable throughout its known range and that the crania do not is perhaps a clue to the mode of inheritance of characters in these mice. Seemingly, color of pelage is inherited independently of characters of the cranium. The relative lack of variability in the crania ofatermay result from uniform environmental conditions, which have served to select for uniform characters in the populations. All of the other wide-ranging subspecies ofB. taylorioccupy more diverse habitats thanater. Secondly, the rather abrupt change in the cline of measured characters of the crania betweenaterandpaulusin central Chihuahua suggests a secondary zone of intergradation. The probable cessation of gene flow in the past between these two subspecies, allowingaterto be isolated for a time, may also, in part, account for the relative lack of variability in the crania ofater.

Natural History

Habitat and numbers.—The habitat occupied by the northern pygmy mouse ranges from sparse grassy areas along rock walls in central México (see Davis, 1944:394), and mesquite-cactus associations in southern Texas (Blair, 1952:242) to heavy stands of grasses such asBoutelouasp.,Andropogonsp.,Hilariasp., and sacaton grass intermixed withYucca glaucain New Mexico, Arizona (see Hoffmeister 1956:281), and Chihuahua. Baker (1951:213) reports the species from 2 km. W El Carrizo, Tamaulipas, in dense grass and weeds at the edge of a cornfield. Hooper (1953:7) recorded the northern pygmy mouse in a cultivated field overgrown with herbaceous vegetation at Pano Ayuctle, Tamaulipas. In the State of Sinaloa, Hooper (1955b:13) obtained specimens in grass and among shrubs and vines bordering a fallow field. The northern pygmy mouse, in general, lives in situations more xerophytic and more grassy than does the southern pygmy mouse.

The northern pygmy mouse, as the southern pygmy mouse, is locally abundant in its geographic range. Stickel and Stickel (op. cit.: 145) pointed out that on the third night of live-trapping in Bexar County, Texas, there was a sudden increase in unmarked pygmy mice trapped. This increase in numbers, after the resident population was seemingly marked, followed a one-half inch rainfall. Collectors from the University of Kansas, myself included, have had similar experiences in trapping these mice. In the Mexican states of Guanajuato, Querétaro, and Jalisco,B. tayloriis one of the commonest small mammals. In New Mexico and Arizona and the Mexican states of Sonora and Sinaloa, nevertheless, these mice are rare.

Stickel and Stickel (loc. cit.) thought that the home range normal forB. tayloriin a grassy habitat was less than 100 square feet, but Blair (1953:10) thought that a complete home range had not been recorded by Stickel and Stickel.

Behavior.—The northern pygmy mouse is crepuscular to nocturnal and where I trapped in northern Mexico was one of the first small rodents to appear in my traps in the evening. Hall and Villa-R (1949:460) recorded this habit in Michoacán. Observations of wild-takenB. tayloriheld in captivity, lend support to its being crepuscular. Captives were rarely active in bright lights, but in diffuse or dim lights the same mice were active.

Blair (1941:381) pointed out that captiveB. t. subaterwere much more tolerant of one another than mice of the genusPeromyscus. He pointed out also that males aided in care of young. In onelitter born in captivity in the course of my study, the female killed the male when the young were four days old. In another instance, the female and two eight-day-old young were killed by the male. Until that time, the male, female, and young had lived together peacefully. In other litters born in captivity, adult males did not harm the other mice.

I have noted, as Blair (loc. cit.) did, thatB. tayloriutters high-pitched squeals in a "singing" posture resembling that of the coyote, yet remains silent when being handled.

The northern pygmy mouse makes runways in the grass, in miniature resembling those ofMicrotus, and often uses runways constructed bySigmodon. A small firm nest of finely shredded plant material (mostly grasses) is constructed in burrows or under logs, rocks, or fallen cactus plants. Thomas (1888:447) recorded nests of fine curly grass and cornsilk. Secondary refuge nests are not uncommon. Thomas (loc. cit.) states, "If other mice live in the same place, the individuals ofBaiomyswatch till others disappear, then suddenly steal part of the other nest and run to their own with it."

Enemies and food.—Little is recorded of the animals that prey upon the northern pygmy mouse. Twente and Baker (1951:120) found remains ofB. tayloriin 16 per cent of barn owl pellets (Tyto alba pratincola) collected 21 mi. SW Guadalajara, Jalisco. Presumably most of the crepuscular and early nocturnal raptorial birds and carnivorous mammals feed on these mice.

Food ofB. tayloriconsists in part of grass seeds and leaves, prickly pear (Opuntiasp.) and the softer exposed parts of roots of vegetation among which the mice reside.

Reproduction.—The northern pygmy mouse breeds throughout the year. The only months in which I have not recorded pregnant females or females with young are June and October. Forty-one records of embryos or young per litter average 2.48 (less than inB. musculus), and range from as few as one to as many as four per litter.

Baiomys taylori allex(Osgood)

Peromyscus allexOsgood, Proc. Biol. Soc. Washington, 17:76-77, March 21, 1904; Elliot, Field Columb. Mus. Publ., 105(6):135, July 1, 1905; Lyon and Osgood, Bull. U. S. Nat. Mus., 62:124, January 15, 1909.

Baiomys taylori allex, Packard, Proc. Biol. Soc. Washington, 71:17, April 11, 1958; Hall and Kelson, The Mammals of North America, 2:659, March 31, 1959 (part).

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

Peromyscus taylori paulus, Osgood, N. Amer. Fauna, 28:255, April 17, 1909 (part).

Baiomys taylori paulus, Miller, Bull. U. S. Nat. Mus., 79:137, December 31, 1912 (part); Miller, Bull. U. S. Nat. Mus., 128:317, April 29, 1924 (part); Ellerman, The Families and Genera of Living Rodents, British Mus. Nat. Hist., 2:402, March 21, 1941 (part); Poole and Schantz, Bull. U. S. Nat. Mus., 178:259, March 6, 1942; Goldman, Smith. Miscl. Coll., 115:373, July 31, 1951 (part); Miller and Kellogg, Bull. U. S. Nat. Mus., 205:512, March 3, 1955 (part); Hall and Kelson, The Mammals of North America, 2:659, March 31, 1959 (part).

Baiomys taylori analogous, Hall and Kelson, Univ. Kansas Publs., Mus. Nat. Hist., 5:367, December 15, 1952 (part).

Type.—Adult male, skin and skull; No. 33429/45452 U. S. Nat. Mus. (Biol. Surv. Coll.); Colima (City), Colima, Republic of México, obtained on March 7, 1892, by E. W. Nelson, original number 2029.Range.—Colima, western lowlands of Michoacán and Jalisco, thence north into southern half of Nayarit, seeFigure 11. Zonal range: arid lower tropical, approximates northern half of the Nayarit-Guerrero Biotic Province of Goldman and Moore (1945:349). Occurs from near sea level in Nayarit, up to 4000 feet in Jalisco.Diagnosis.—Size small for the species; dorsal ground color pale grayish-brown, near Isabella color; mid-dorsal region washed with blackish, individual guard hairs black to base, other hairs black-tipped with subterminal light olive bands, Neutral Gray at base; laterally, black-tipped hairs less abundant, hairs grayish-white to base; venter Pale Gull Gray to whitish, distal half of individual hairs white, proximal half Neutral Gray; hairs in regions of throat and chin white to base; facial region colored like dorsum, becoming paler below eye; in region of mouth, hairs white to base; dorsalmost vibrissae black to base, others white to base; ears flesh-colored, sparsely haired; tail unicolored, sparsely haired for the species; dark blotches on tail of some series (particularly the paratypical series); dorsal and ventral parts of forefeet and hind feet flesh-colored, whitish to gray in some series. Slightly smaller in most cranial dimensions. Maxillary part of zygoma forming almost a right angle with rostrum, rather than tapering at less than a right angle to rostrum; supraoccipital rounded posteriorly rather than indented on each side of foramen magnum; cranium, relative to length of rostrum, more nearly square; interparietal large relative to size of cranium. Average and extreme measurements of five adults from 2 mi. SSE Autlán are as follows: total length, 100.0 (93-107); length of tail vertebrae, 40.0 (37-44); length of body, 60.0 (56-63); length of hind foot, 14.0 (14); length of ear from notch, 10.5 (10-11); occipitonasal length, 17.3 (16.8-17.9); zygomatic breadth, 9.1 (8.7-9.4); postpalatal length, 6.3 (6.0-6.6); least interorbital breadth, 3.4 (3.3-3.5); length of incisive foramina, 3.9 (3.8-4.0); length of rostrum, 5.5 (5.2-5.8); breadth of braincase, 8.6 (8.0-8.9); depth of cranium, 6.4 (6.0-6.7); alveolar length of maxillary tooth-row, 3.0 (2.8-3.1); for photographs of skull, seePlate 1iandPlate 4a.Comparisons.—For comparisons withB. t. canutus, see account of that subspecies. FromB. t. analogous,B. t. allexdiffers in: external and cranial dimensions less; dorsal coloration paler; tail and ears paler and less hairy; dorsum and belly paler; dorsal and ventral parts of forefeet and hind feet paler; median parts of incisive foramina less constricted on either side of midline and wider open laterally; interparietal larger in relation to skull; interorbital breadth greater relative to occipitonasal length.[Pg 635]B. t. allexdiffers fromB. t. paulusas follows: dorsum gray with yellowish-brown wash rather than fawn to buff; tail unicolored in most series, less hairy; hind feet flesh-colored to light sooty, rather than whitish; rostrum slightly longer relative to occipitonasal length; incisive foramina differ from those ofpaulusin much the same way as fromanalogous.

Type.—Adult male, skin and skull; No. 33429/45452 U. S. Nat. Mus. (Biol. Surv. Coll.); Colima (City), Colima, Republic of México, obtained on March 7, 1892, by E. W. Nelson, original number 2029.

Range.—Colima, western lowlands of Michoacán and Jalisco, thence north into southern half of Nayarit, seeFigure 11. Zonal range: arid lower tropical, approximates northern half of the Nayarit-Guerrero Biotic Province of Goldman and Moore (1945:349). Occurs from near sea level in Nayarit, up to 4000 feet in Jalisco.

Diagnosis.—Size small for the species; dorsal ground color pale grayish-brown, near Isabella color; mid-dorsal region washed with blackish, individual guard hairs black to base, other hairs black-tipped with subterminal light olive bands, Neutral Gray at base; laterally, black-tipped hairs less abundant, hairs grayish-white to base; venter Pale Gull Gray to whitish, distal half of individual hairs white, proximal half Neutral Gray; hairs in regions of throat and chin white to base; facial region colored like dorsum, becoming paler below eye; in region of mouth, hairs white to base; dorsalmost vibrissae black to base, others white to base; ears flesh-colored, sparsely haired; tail unicolored, sparsely haired for the species; dark blotches on tail of some series (particularly the paratypical series); dorsal and ventral parts of forefeet and hind feet flesh-colored, whitish to gray in some series. Slightly smaller in most cranial dimensions. Maxillary part of zygoma forming almost a right angle with rostrum, rather than tapering at less than a right angle to rostrum; supraoccipital rounded posteriorly rather than indented on each side of foramen magnum; cranium, relative to length of rostrum, more nearly square; interparietal large relative to size of cranium. Average and extreme measurements of five adults from 2 mi. SSE Autlán are as follows: total length, 100.0 (93-107); length of tail vertebrae, 40.0 (37-44); length of body, 60.0 (56-63); length of hind foot, 14.0 (14); length of ear from notch, 10.5 (10-11); occipitonasal length, 17.3 (16.8-17.9); zygomatic breadth, 9.1 (8.7-9.4); postpalatal length, 6.3 (6.0-6.6); least interorbital breadth, 3.4 (3.3-3.5); length of incisive foramina, 3.9 (3.8-4.0); length of rostrum, 5.5 (5.2-5.8); breadth of braincase, 8.6 (8.0-8.9); depth of cranium, 6.4 (6.0-6.7); alveolar length of maxillary tooth-row, 3.0 (2.8-3.1); for photographs of skull, seePlate 1iandPlate 4a.

Comparisons.—For comparisons withB. t. canutus, see account of that subspecies. FromB. t. analogous,B. t. allexdiffers in: external and cranial dimensions less; dorsal coloration paler; tail and ears paler and less hairy; dorsum and belly paler; dorsal and ventral parts of forefeet and hind feet paler; median parts of incisive foramina less constricted on either side of midline and wider open laterally; interparietal larger in relation to skull; interorbital breadth greater relative to occipitonasal length.

[Pg 635]

B. t. allexdiffers fromB. t. paulusas follows: dorsum gray with yellowish-brown wash rather than fawn to buff; tail unicolored in most series, less hairy; hind feet flesh-colored to light sooty, rather than whitish; rostrum slightly longer relative to occipitonasal length; incisive foramina differ from those ofpaulusin much the same way as fromanalogous.

Remarks.—Osgood (1909:255-256) dismissed as taxonomically unimportant the differences in color of pelage and size of cranium that he observed between the specimens from Colima (City), Colima, representative ofallexand those representingpaulusand chose to synonomizeallexwithpaulus. The differences that Osgood (loc. cit.) deemed "… scarcely worthy of recognition …," are, in fact, not only worthy of recognition, but also important in an understanding of the evolution ofBaiomys taylori(see speciationp. 659). Recently, I (1958b:17-18) studied ten specimens from Colima (City), Colima, and chose to regardPeromyscus [= Baiomys] allexas a subspecies. I suggested (loc. cit.) that the geographic range ofB. t. allexmight encompass the southern part of Nayarit, and western Jalisco. Subsequent study of specimens from these areas reveals that the populations there are referable toallex. Most of the specimens obtained from these areas, however, merit special comment.

In color of pelage, those populations from south of the Río Grande de Santiago and northwest of Guadalajara (4 mi. SE Ahuacatlán; 1 mi. E Ixtlán; Etzatlán) show evidence of intergradation withpaulusto the east and south (Magdalena, Tequila, and Tala, Jalisco), and with populations more closely adjacent to the south bank of that river. Intergradation is indeed complex in this area. Specimens from some localities seem to be intergrades betweenallexandpaulus; from other localities, some specimens are referable toallex, and the others topaulus; from still other localities, all specimens are referable toallex.

A series of 39 specimens from 1 mi. SSE Ameca, 4000 ft., Jalisco, are uniformly grayish-brown. This series averages grayer than paratypes ofallex. There is little, if any, difference between the series from 1 mi. SSE Ameca and paratypes ofallexin external size of body, hind foot, length of ear, and size and conformation of the cranium. Populations from Ameca and vicinity might be expected to average considerably larger inasmuch as they occur at higher altitudes (see Bergman's Rule,p. 609) then the material from the lower coastal plains to the south in Colima and Michoacán, and at lower elevations in the west in Jalisco and Nayarit. The means of externaland cranial measurements are not significantly different between the specimens from the highlands and those from the lowlands. In the area of Ameca where the two speciesB. musculusandB. taylorioccur together, interspecific competition seems to have limited, perhaps even reduced, size of external and cranial parts oftaylori(seep. 660).

In color, specimens from the northern part of the valley of the Río Tepalcatepec (10 mi. S, 1 mi. W Apatzingán) in Michoacán resemble paratypes ofallex. Intergradation probably occurs to the north withanalogous.

In the eight specimens from 13 mi. E and 1 mi. N Talpa de Allendé, the skull, as reflected in occipitonasal length and zygomatic breadth relative to length of body, is larger than in other specimens here assigned toallex. The median part of the belly of the eight specimens is buff-colored rather than whitish-gray as in typicalallex; the mid-dorsal region also averages darker than in any other specimens referred toallex. Additional specimens are needed from this and closely adjacent areas, especially to the west on the coastal plain, in order to determine more accurately the taxonomic status of the mice there. At present, it seems best to refer them toallex. Possibly the population represented by the eight specimens is an incipient subspecies.

There is no evidence of hybridization or intergradation of populations ofB. t. allexwith any population ofB. musculuswhere the two species occur together.

Specimens examined.—Total 233, all from the Republic of México, distributed as follows:Nayarit: 3 mi. SE Mirador, 7; 2mi. S. Compostela, 2900 ft., 5; 4mi. N Santa Isabel, 3800 ft., 2[25];2 mi. N Santa Isabel, 3800 ft., 22[25];4 mi SE Ahuacatlán, 5200 ft., 2[26];1 mi. E Ixtlán, 4000 ft., 13[25]; 1 mi. E Ixtlán del Río, 3700 ft., 1; 2 mi. WNW Valle de Banderas, near sea level, 1.Jalisco: Arroyo de Gavalán, 16[28]; Etzatlán, 6[27];Mascota, 3900 ft., 6[27];7 mi W Ameca, 15[25];6 mi. W Ameca, 15[25];3 mi. W Ameca, 5[25]; Ameca, 4000 ft., 11[27];1 mi. SSE Ameca, 4000 ft., 38; 2 mi. N Resolana, 1500 ft., 28[25]; 13 mi. E, 1 mi. N Talpa de Allendé, 8; 2 mi. SSE Autlán, 5; 1 mi. N San Gabriel, 4000 ft., 1[25]; Las Canoas, l[28].Colima: Type locality, 10[27](including the type).Michoacán: 9 mi. S Lombardia, 1500 ft., 1;3 mi. W Apatzingán, 1000 ft, 1; Apatzingán, 3[25]; 10 mi. S, 1 mi. W Apatzingán, 800 ft., 10.Marginal records.—Nayarit: 3 mi. SE Mirador; 1 mi. E Ixtlán del Río.Jalisco: Etzatlán; Ameca; 2 mi. N Resolana; Las Canoas.Michoacán: 9 mi. S Lombardia; 10 mi. S, 1 mi. W Apatzingán.Colima: type locality.Nayarit: Valle de Banderas.

Marginal records.—Nayarit: 3 mi. SE Mirador; 1 mi. E Ixtlán del Río.Jalisco: Etzatlán; Ameca; 2 mi. N Resolana; Las Canoas.Michoacán: 9 mi. S Lombardia; 10 mi. S, 1 mi. W Apatzingán.Colima: type locality.Nayarit: Valle de Banderas.

[25]Univ. Michigan, Museum of Zoology.

[26]California Academy of Sciences.

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

[28]American Museum of Natural History.

Baiomys taylori analogous(Osgood)

Peromyscus taylori analogousOsgood, N. Amer. Fauna, 28:256, April 17, 1909 (part); Elliott, Check-List Mamm., N. Amer. Cont., West Indies and Neighboring Seas, Suppl., Amer. Mus. Nat. Hist., p. 44, January 8, 1917.

Baiomys taylori analogous, 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, British Mus. Nat. Hist., 2:402, March 21, 1941; Poole and Schantz, Bull. U. S. Nat. Mus., 178:259, March 6, 1942; Davis, Jour. Mamm., 25:394, December 12, 1944; Hooper, Jour. Mamm., 28:50, February 15, 1947; Hall and Villa-R., Univ. Kansas Publs., Mus. Nat. Hist., 1:460, December 27, 1949; Hall and Villa-R., Anal. del Inst. Biol., 21:196, September 28, 1950; Goldman, Smith. Miscl. Coll., 114:373, July 31, 1951 (part); Hall and Kelson, Univ. Kansas Publs., Mus. Nat. Hist., 5:367, December 15, 1952 (part); Villa-R., Anal. del Inst. Biol., 23:435, May 20, 1953; Miller and Kellogg, Bull. U. S. Nat. Mus., 205:512, March 3, 1955; Hooper, Occas. Papers Mus. Zool. Univ. Michigan, 565:13, March 31, 1955; Packard, Proc. Biol. Soc. Washington, 71:17, April 11, 1958.

Peromyscus musculus brunneus, Elliot, Field Columb. Mus. Publ., 115(8):203, 1907 (part).

Peromyscus musculus[musculus], Osgood, N. Amer. Fauna, 28:258, April 17, 1909 (part).

Baiomys musculus musculus, 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).

Baiomys taylori taylori, Dalquest, Louisiana State Univ. Studies (Biol. Sci. Ser.), 1:155, December 28, 1953 (part); Hall and Kelson, The Mammals of North America, 2:660, March 31, 1959 (part).

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

Baiomys musculus musculus, Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part).

Type.—Adult male, skin and skull; No. 120261 U. S. Nat. Mus. (Biol. Surv. Coll.); Zamora, Michoacán, Republic of México, obtained on January 15, 1903, by E. W. Nelson, and E. A. Goldman, original number 15764.Range.—Central and eastern Jalisco south into Michoacán, east through Guanajuato, Querétaro, thence into Estado México, and Distrito Federal, and west-central Veracruz, seeFigure 11. Zonal range: approximately the Transverse Volcanic Biotic Province of Moore (1945:218) and of Goldman and Moore (1945:349). Occurs from 5000 feet, 7 mi. S Ocotlán, Jalisco, up to 8000 feet in Ixtapalapa, Distrito Federal.Diagnosis.—Size large for the species; dorsum dark Sepia to near blackish medially in freshly taken specimens (Sepia fading to near Fuscous in prepared specimens); belly slaty-gray, hairs Deep Neutral Gray near tips and Dusky Neutral Gray at bases; hairs on back black-tipped with subterminal band of Ochraceous-Tawny (guard hairs blackish to base); hairs of throat and chin white-tipped, gray at bases; dorsal vibrissae black, ventral and anteriormost vibrissae white; hairs on face and sides black-tipped, and Ochraceous-Tawny at base; ears sparsely haired, individual hairs grayish, blackish, and ochraceous;[Pg 638]tail sooty to blackish dorsally, lighter ventrally; forefeet and hind feet sooty brown on dorsal and ventral surface. Skull relatively broad interorbitally; zygoma broad and squared; cranium larger in all dimensions than in most other subspecies. Average and extreme measurements of 10 adults from 1 mi. S, 11 mi. W Zamora, 5400 ft., Michoacán, are: total length, 109.4 (102-121); length of body, 64.3 (58-72); length of tail, 44.9 (39-51); length of hind foot, 14.6 (14-15); occipitonasal length, 18.0 (17.5-18.6); zygomatic breadth, 9.4 (9.1-9.7); postpalatal length, 6.6 (6.2-7.2); least interorbital breadth, 3.5 (3.3-3.8); length of incisive foramina, 4.0 (3.8-4.2); length of rostrum, 6.2 (5.8-6.5); breadth of braincase, 8.7 (8.5-8.9); depth of cranium, 6.6 (6.3-6.9); alveolar length of maxillary tooth-row, 3.1 (3.0-3.3); for photographs of skull, seePlate 2aandPlate 4b.Comparisons.—For comparisons withB. t. allex,B. t. canutus,B. t. paulus, andB. t. fuliginatus, see accounts of those subspecies. FromB. t. taylori,B. t. analogousdiffers as follows: sides and dorsum darker, differing most in freshly prepared specimens; dorsal surface of forefeet and hind feet darker; basal part of hairs on belly darker gray; frontal bones less constricted, causing less taper anteriorly in interorbital space; interparietal wider transversely; basioccipital more expanded laterally, narrowing more abruptly at suture between basioccipital and basisphenoid.

Range.—Central and eastern Jalisco south into Michoacán, east through Guanajuato, Querétaro, thence into Estado México, and Distrito Federal, and west-central Veracruz, seeFigure 11. Zonal range: approximately the Transverse Volcanic Biotic Province of Moore (1945:218) and of Goldman and Moore (1945:349). Occurs from 5000 feet, 7 mi. S Ocotlán, Jalisco, up to 8000 feet in Ixtapalapa, Distrito Federal.

Diagnosis.—Size large for the species; dorsum dark Sepia to near blackish medially in freshly taken specimens (Sepia fading to near Fuscous in prepared specimens); belly slaty-gray, hairs Deep Neutral Gray near tips and Dusky Neutral Gray at bases; hairs on back black-tipped with subterminal band of Ochraceous-Tawny (guard hairs blackish to base); hairs of throat and chin white-tipped, gray at bases; dorsal vibrissae black, ventral and anteriormost vibrissae white; hairs on face and sides black-tipped, and Ochraceous-Tawny at base; ears sparsely haired, individual hairs grayish, blackish, and ochraceous;[Pg 638]tail sooty to blackish dorsally, lighter ventrally; forefeet and hind feet sooty brown on dorsal and ventral surface. Skull relatively broad interorbitally; zygoma broad and squared; cranium larger in all dimensions than in most other subspecies. Average and extreme measurements of 10 adults from 1 mi. S, 11 mi. W Zamora, 5400 ft., Michoacán, are: total length, 109.4 (102-121); length of body, 64.3 (58-72); length of tail, 44.9 (39-51); length of hind foot, 14.6 (14-15); occipitonasal length, 18.0 (17.5-18.6); zygomatic breadth, 9.4 (9.1-9.7); postpalatal length, 6.6 (6.2-7.2); least interorbital breadth, 3.5 (3.3-3.8); length of incisive foramina, 4.0 (3.8-4.2); length of rostrum, 6.2 (5.8-6.5); breadth of braincase, 8.7 (8.5-8.9); depth of cranium, 6.6 (6.3-6.9); alveolar length of maxillary tooth-row, 3.1 (3.0-3.3); for photographs of skull, seePlate 2aandPlate 4b.

Comparisons.—For comparisons withB. t. allex,B. t. canutus,B. t. paulus, andB. t. fuliginatus, see accounts of those subspecies. FromB. t. taylori,B. t. analogousdiffers as follows: sides and dorsum darker, differing most in freshly prepared specimens; dorsal surface of forefeet and hind feet darker; basal part of hairs on belly darker gray; frontal bones less constricted, causing less taper anteriorly in interorbital space; interparietal wider transversely; basioccipital more expanded laterally, narrowing more abruptly at suture between basioccipital and basisphenoid.

Remarks.—The pelage ofanalogousbecomes paler with wear as pointed out by Osgood (1909:257). A paratype, U. S. Nat. Mus. 120260, and several specimens from 1 mi. S, 11 mi. W Zamora, Michoacán, are grayish rather than brownish-black. All of these are old adults having the terminal black parts of the hairs on the dorsum nearly worn away. Excluding such grayish individuals,B. t. analogous, likeB. t. subaterandB. t. fuliginatus, is uniformly brownish-black. Bothanalogousandfuliginatusoccur in relatively high mountainous country on dark soils or pedregals, and all three of the aforementioned subspecies occur in zones of high relative humidity.

B. t. analogousintergrades withB. t. paulus(see account of that subspecies) andB. t. allexsouth and west of Lago de Chapala in Jalisco. Additional specimens are needed from Querétaro and San Luis Potosí in order to ascertain whether or notB. t. analogousintergrades withB. t. fuliginatusorB. t. taylori. Specimens from western Jalisco, in the past referred toB. t. analogous, are referable toB. t. allex(see account of that subspecies). Specimens obtained west of, and bordering, the Río del Naranjo in Jalisco show a mixture of characters of bothB. t. allexandB. t. analogous. For example, specimens from 2 mi. N Ciudad Guzmán resembleanalogouson the dorsum, whereas, on the belly, the individual hairs are white-tipped, pale gray at the base, and in over-all appearance are whitish-gray, unlike typicalanalogous(being likeallexinstead). The dorsal surface of the forefeet are sooty to light brownish (as inanalogous),whereas, the hind feet are flesh-colored (as inallex). Another series of specimens from 4 mi. W León, Guanajuato, are intergrades betweenB. t. analogousandB. t. paulus. These specimens are grayish to brownish on the dorsum, have sooty forefeet and hind feet (more nearly as inanalogousthan inpaulus), are grayish-white on the venter, and have a distinctly bicolored tail (resembling that ofpaulusmore than that ofanalogous). When the average of cranial characters is considered, both series are best referred toanalogous.

Hooper (1947:50) pointed out that specimens from the pedregal San Gerónimo, Distrito Federal, were more nearly black than topotypes and generally showed less brownish hues typical ofanalogous. I have examined this series and several others from this area (see Specimens examined,p. 640) and am convinced that these populations average darker. Actually, the dorsum is more nearly black and the venter is more buffy than in typicalanalogous. The hairs of these individuals average longer than in other populations ofanalogous. Skulls of the specimens from the pedregal are indistinguishable from those of paratypes ofanalogous. The populations from the Distrito Federal seem to be incipient subspecies.

Specimens examined.—Total 696, all from the Republic of México, distributed as follows:San Luis Potosí: Hacienda Capulín, 5[33];3.3 mi. N Tamazunchale, by-road, 2[34]; 1 mi. N Tamazunchale, 700 ft., 1[35].Veracruz: Acultzingo, 4[29], 1[31].Jalisco: 1 mi. S Jalostotitlán, 5700 ft., 5; 7 mi. NW Tepatitlán, 3[29];6 mi. N, 4 mi. E Tepatitlán, 6400 ft., 25;21/2mi. E Tepatitlán, 6200 ft., 15;2 mi. S,1/2mi. W Tepatitlán, 9;near Tepatitlán, 2;5 mi. SW Arrandas, 6700 ft., 6;2 mi. E Zapotlanejo, 23;21/2mi. E Puente Grande(51/2mi. SW Zapotlanejo), 3;8 mi. S Guadalajara, 10[29];3 mi. ENE Santa Cruz de las Flores, 9;4 mi. NE Ocotlán, 5050 ft., 18;13 mi. S, 91/2mi. W Guadalajara, 1;2 mi. WNW Ocotlán, 5000 ft., 15; 13 mi. S, 15 mi. W Guadalajara, 2;Ocotlán, 5000 ft., 8[30];1 mi. S Ocotlán, 5000 ft., 12; 27 mi. S, 12 mi. W Guadalajara, 9;11/2mi. N Mazatmitla, 6[29];1/2mi. NW Mazatmitla, 4;3 mi. WSW Mazatmitla, 4; 2 mi. N Ciudad Guzmán, 5000 ft., 18.Guanajuato: 4 mi. N, 5 mi. W León, 7000 ft., 25; 5 mi. S Salamanca, 2[29];5 mi. E Celaya, 6000 ft., 6;1 mi. E Yuriria, 5725 ft., 3; Salvatierra, 5775 ft., 8;NE edge Acambaro, 6050 ft., 10;Acambaro, 3[30].Querétaro: Tolimán, 7[30]; 6 mi. E Querétaro, 6550 ft., 37.Hidalgo: Tula, 2050 m., 1[31].Michoacán:2 mi. E La Palma, SE side Lago de Chapala, 7; type locality, 4000 ft., 10[30](including the type);9 mi. E Zamora(Camenaro), 2[29];1 mi. S, 11 mi. W Zamora, 5400 ft., 17; S Cuitzeo, 36[29];Jiquilpan, 4800 ft., 15;11 mi. W Jiquilpan, 6700 ft., 2;1 mi. E Jiquilpan, 7;1 mi. E Zinapecuaro, 6300 ft., 17;41/2mi. NE Tarequato(Tarecuato), 6600 ft, 1;Tanganciguaro(Tangancicuaro), 5500 ft., 4;2 mi. N Tarecuato, 7200 ft., 1;2 mi. S Maravatio, 6650 ft, 6;2 mi. SE Zacapu, 6600 ft., 11;1 mi. N Tinquindin(Tinguindin), 6300 ft., 2;3 mi. E Morelia, 6600 ft., 3;11 mi. E, 2 mi. S Morelia, 1; 2 mi. SE Hidalgo (Villa Hidalgo), 6;11/2mi. N Los Reyes, 1;E Los Reyes, 18[29];Los Reyes, 8[30];3 mi. W, 1 mi. N Pátzucuaro, 6600 ft., 2;N Pátzucuaro, 2[29];Pátzucuaro9[31], 4[30], 4[29]; Uruapan, 1[29];E Uruapan, 12;21/2mi. E Uruapan(La Presca), 2[29]; 2 mi. SW Zitacuaro, 1; 1 mi. E, 6 mi. S Tacámbaro, 4000 ft., 11[37];La Huacana, 1[30].Mexico: Templo del Sol, Pyramídes de San Juan,[Pg 640]Teotihuacán, 8000 ft., 1;31 km. E México City, 7500 ft., 11[36];17 km. E México City, 7500 ft, 1[36];Cerro La Caldera, 11 mi. ESE México, 2350 m., 5; 4 km. ENE Tlalmanalco, 2290 m., 9;Hacienda Córdoba(Córdova), 6.Mexico, D. F.:Cerro de la Estrella, Ixtapalapa, 2450 m., 1;3/4mi. S, 1 mi. E Churubusco, 2400 m., 2;5 km. S México City, South of Cd. Universitaria, l[32];Pedregal San Angel,2.6 mi. S Monumento a Obregón, 2;El Pedregal, 1 km. S San Angel, 2260 m., 1;Falda SW Cerro Zacatepec, 3.9 mi. SW Monumento a Obregón, 1;2 mi. N Tlalpan, Zacayuca, 2380 m., 5;Tlalpan(Pedregal), 2400 m., 21[31];San Gerónimo, 37[29], 6[38];Santa Rosa, 2700 m., 1[32];Tlalpan, 8;3/4mi. SW Las Fuentes, Tlalpan, 2450 m., 25[30];Tepepán, 6[29];Rancho La Noria, 1 mi. W Xochimilco, 2270 m., 4;500 meters N Xochitepec, 2250 m., 7; 200 m. N San Mateo Xalpa (Jalpa), 2390 m., 2.Marginal records.—San Luis Potosí: Hacienda Capulín; 1 mi. N Tamazunchale.Hidalgo: Tula, 2050 m.Mexico: Templo del Sol, Pyramídes de San Juan, Teotihuacán.Veracruz: Acultzingo.Mexico: 4 km. ENE Tlalmanalco.Mexico, D. F.: 200 m. N San Mateo Xalpa (Jalpa), 2390 m.Michoacán: 2 mi. SW Zitacuaro; 1 mi. E, 6 mi. S Tacámbaro; Uruapan.Jalisco: 2 mi. N Ciudad Guzmán; 27 mi. S, 12 mi. W Guadalajara; 13 mi. S, 15 mi. W Guadalajara; 7 mi. NW Tepatitlán; 1 mi. S Jalostotitlán, 5700 ft.Guanajuato: 4 mi. N, 5 mi. W León.Querétaro: 6 mi. E Querétaro, 6550 ft.; Tolimán.

Marginal records.—San Luis Potosí: Hacienda Capulín; 1 mi. N Tamazunchale.Hidalgo: Tula, 2050 m.Mexico: Templo del Sol, Pyramídes de San Juan, Teotihuacán.Veracruz: Acultzingo.Mexico: 4 km. ENE Tlalmanalco.Mexico, D. F.: 200 m. N San Mateo Xalpa (Jalpa), 2390 m.Michoacán: 2 mi. SW Zitacuaro; 1 mi. E, 6 mi. S Tacámbaro; Uruapan.Jalisco: 2 mi. N Ciudad Guzmán; 27 mi. S, 12 mi. W Guadalajara; 13 mi. S, 15 mi. W Guadalajara; 7 mi. NW Tepatitlán; 1 mi. S Jalostotitlán, 5700 ft.Guanajuato: 4 mi. N, 5 mi. W León.Querétaro: 6 mi. E Querétaro, 6550 ft.; Tolimán.

[29]Univ. Michigan, Museum of Zoology.

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

[31]Chicago Natural History Museum.

[32]American Museum of Natural History.

[33]Museum of Natural History, Louisiana State University.

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

[35]The Museum, Michigan State Univ.

[36]Texas A & M, Cooperative Wildlife Research Collection.

[37]Univ. California, Mus. Vert. Zoology.

[38]University of Florida Collections.

Baiomys taylori ater(Blossom and Burt)

Baiomys taylori aterBlossom and Burt, Occas. Papers Mus. Zool., Univ. Michigan, 465:2, October 8, 1942; Blair and Blossom, Contrib. Lab. Vert. Biol., Univ. Michigan, 40:1, March, 1948; Hoffmeister and Goodpaster, Ill. Biol. Monogr., 24(1):115, December 31, 1954; Miller and Kellogg, Bull. U. S. Nat. Mus., 205:511, March 3, 1955; Hoffmeister, Amer. Midland Nat., 55:281, April, 1956; Packard, Jour. Mamm., 40:146, February 20, 1959; Hall and Kelson, The Mammals of North America, 2:659, March 31, 1959 (part).

Peromyscus taylori paulus, Osgood, N. Amer. Fauna, 28:256, April 17, 1909 (part).

Baiomys taylori[ater], Justice, Jour. Mamm., 38:520, November 20, 1957.

Type.—Adult male, skin and skull; No. 85425, University of Michigan, Museum of Zoology; 7 mi. W Hereford, Cochise County, Arizona, obtained on March 25, 1941, by Philip M. Blossom, original number 2195.Range.—Southeastern Arizona, north to Graham County, thence east to the Animas Valley, Hidalgo County, New Mexico; south to northern Chihuahua and northwest to the southern border of Cochise County, Arizona, seeFigure 11. Zonal range: largely lower Sonoran (Apachian Biotic Province of Dice, 1943:56). Occurs from 4300 feet in Chihuahua up to 6200 feet in New Mexico.Diagnosis.—Size medium for the species; dorsum between Mummy Brown and Prouts Brown; individual tips of hairs intermixture of black and Ochraceous-Tawny, bases of all hairs slate-gray; sides of body and face, Buffy Brown to Cinnamon Brown; belly Cinnamon Buff, proximal half of individual hairs Deep Neutral Gray, distal half white; in region of throat, proximal[Pg 641]fourth of individual hairs gray, distal three-fourths white; dorsal vibrissae black to base, ventral vibrissae white to base; tail brownish above, gray below; dorsal and ventral surface of forefeet and hind feet buffy to gray; interparietal somewhat compressed anteroposteriorly. Average and extreme cranial measurements of 15 adults from 91/2mi. W New Mexico State Line, 51/2mi. N Mexican border, Cochise County, Arizona, are as follows: occipitonasal length, 18.0 (17.5-18.6); zygomatic breadth, 9.5 (9.2-9.9); postpalatal length, 6.6 (6.0-7.1); least interorbital breadth, 3.6 (3.4-3.8); length of incisive foramina, 4.0 (3.8-4.2); length of rostrum, 6.1 (5.7-6.4); breadth of braincase, 8.6 (8.4-9.1); depth of cranium, 6.5 (6.3-6.9); alveolar length of maxillary tooth-row, 3.2 (3.1-3.4). Average and extreme external measurements for six adults from 9 mi. W Hereford, Cochise County, are as follows: total length, 106.3 (98-115); length of tail vertebrae, 42.3 (39-46); length of body, 64 (59-69); length of hind foot, 13.6 (13-14.2); length of ear from notch, 11.1 (10.5-11.5); for photographs of skull, seePlate 2b, andPlate 4c.Comparisons.—For comparisons withB. t. canutus, see account of that subspecies. FromB. t. paulus, the subspecies to the southeast,B. t. aterdiffers in: dorsum darker brown; tail less strikingly bicolored; belly buffy rather than whitish to white-gray; forefeet and hind feet darker dorsally and ventrally; posterior margin of basioccipital bowed anteriorly in a broad U-shape with a secondary small median anteriorly directed U-shaped curve, rather than bowed anteriorly in a simple U-shape; interparietal more compressed anteroposteriorly; coronoid process of mandible so acutely recurved that tip of coronoid points posteroventrally and appears sickle-shaped.

Range.—Southeastern Arizona, north to Graham County, thence east to the Animas Valley, Hidalgo County, New Mexico; south to northern Chihuahua and northwest to the southern border of Cochise County, Arizona, seeFigure 11. Zonal range: largely lower Sonoran (Apachian Biotic Province of Dice, 1943:56). Occurs from 4300 feet in Chihuahua up to 6200 feet in New Mexico.

Diagnosis.—Size medium for the species; dorsum between Mummy Brown and Prouts Brown; individual tips of hairs intermixture of black and Ochraceous-Tawny, bases of all hairs slate-gray; sides of body and face, Buffy Brown to Cinnamon Brown; belly Cinnamon Buff, proximal half of individual hairs Deep Neutral Gray, distal half white; in region of throat, proximal[Pg 641]fourth of individual hairs gray, distal three-fourths white; dorsal vibrissae black to base, ventral vibrissae white to base; tail brownish above, gray below; dorsal and ventral surface of forefeet and hind feet buffy to gray; interparietal somewhat compressed anteroposteriorly. Average and extreme cranial measurements of 15 adults from 91/2mi. W New Mexico State Line, 51/2mi. N Mexican border, Cochise County, Arizona, are as follows: occipitonasal length, 18.0 (17.5-18.6); zygomatic breadth, 9.5 (9.2-9.9); postpalatal length, 6.6 (6.0-7.1); least interorbital breadth, 3.6 (3.4-3.8); length of incisive foramina, 4.0 (3.8-4.2); length of rostrum, 6.1 (5.7-6.4); breadth of braincase, 8.6 (8.4-9.1); depth of cranium, 6.5 (6.3-6.9); alveolar length of maxillary tooth-row, 3.2 (3.1-3.4). Average and extreme external measurements for six adults from 9 mi. W Hereford, Cochise County, are as follows: total length, 106.3 (98-115); length of tail vertebrae, 42.3 (39-46); length of body, 64 (59-69); length of hind foot, 13.6 (13-14.2); length of ear from notch, 11.1 (10.5-11.5); for photographs of skull, seePlate 2b, andPlate 4c.

Comparisons.—For comparisons withB. t. canutus, see account of that subspecies. FromB. t. paulus, the subspecies to the southeast,B. t. aterdiffers in: dorsum darker brown; tail less strikingly bicolored; belly buffy rather than whitish to white-gray; forefeet and hind feet darker dorsally and ventrally; posterior margin of basioccipital bowed anteriorly in a broad U-shape with a secondary small median anteriorly directed U-shaped curve, rather than bowed anteriorly in a simple U-shape; interparietal more compressed anteroposteriorly; coronoid process of mandible so acutely recurved that tip of coronoid points posteroventrally and appears sickle-shaped.

Remarks.—Blossom and Burt (1942:1) describedB. t. ateras the darkest of the known subspecies. It is dark, but specimens from some parts of the ranges ofB. t. analogous,B. t. fuliginatus, andB. t. subaterexceed in melanins the darkest individuals ofater. Blair and Blossom (1948:5) also concluded by the use of an Ives tint photometer thatB. t. subaterwas significantly darker thanB. t. ater.

When paratypes ofaterand specimens ofB. t. paulusare compared, the darkest individuals ofaterexceed but slightly the darkest ofpaulus. The darkest specimens ofpaulusoccur in southern Zacatecas, and northern Jalisco, and the palest of the series are in northern Durango and southern Chihuahua. When paratypes ofaterandpaulusare compared, the difference in color is readily distinguishable. Specimens from 11/2mi. N San Francisco, in northern Chihuahua, appear to be intermediate in color betweenaterandpaulusexcept for a faint tinge of buff ventrally. In characters of the crania, these specimens resembleaterand are referred to that subspecies. A slightly different pattern of color is present in pygmy mice from the Peloncillo Mountains and the Animas Valley of New Mexico; the upper parts resemble those of paratypes ofater, but the venter has only the faintest suggestion of thebuffy wash. Crania of these specimens from New Mexico are inseparable from those of paratypes ofater, and the specimens are, therefore, referred toater.

When specimens are arranged by localities from Arizona east into southern New Mexico, thence south into Chihuahua and Durango, gradual intergradation in color is evident from dark in the north to pale browns in the south, whereas, size and shape of interparietal and size and shape of coronoid process of the lower jaw divide quite distinctly into two morphological types in central Chihuahua.

Cranial variation in size and proportion among adults is slight throughout the range ofatercompared to variation detected in other subspecies ofBaiomys taylori. Perhaps such a relatively stable pattern of characters of the crania reflects the homogeneity of the gene pool, with respect to these characters, of the populations sampled. The fact that the color of the pelage of this subspecies varies considerable throughout its known range and that the crania do not is perhaps a clue to the mode of inheritance of characters in these mice. Seemingly, color of pelage is inherited independently of characters of the cranium. The relative lack of variability in the crania ofatermay result from uniform environmental conditions, which have served to select for uniform characters in the populations. All of the other wide-ranging subspecies ofB. taylorioccupy more diverse habitats thanater. Secondly, the rather abrupt change in the cline of measured characters of the crania betweenaterandpaulusin central Chihuahua suggests a secondary zone of intergradation. The probable cessation of gene flow in the past between these two subspecies, allowingaterto be isolated for a time, may also, in part, account for the relative lack of variability in the crania ofater.

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