distributed as follows: PUEBLA: 2 mi. S Atlixco, 5800 ft., 1; _1 mi. SSW
Tilapa_, 5800 ft., 2; _6 mi. SW Izucar de Matemores_, 7; _Piaxtla_, 3900
ft., 4[18]; Acatlan, 4100 ft., 1. MORELOS: 5 mi. W Tepoztlan, 6000 ft.,
7[19]; _1 mi. W Tepoztlan_, 6000 ft., 9[19]; _2 mi. SW Tepoztlan_, 7000
ft., 1[20]; _Cuernvaca_, 9[19]; _6 mi. W Yautepec_, 4500 ft., 1[20];
_Yautepec_, 12[19]; _3 mi. N Alpuyeca_, 4000 ft., 2[20]; _Puente de
Ixtla_, 2[19]; _Tetecala_, 4[21]; _2 km. S Jonacatepec_, 4500 ft., 6[20];
_type locality_, 6 (including the type). GUERRERO: _Yerbabuena_, 1800
m., 1; _Cueva de tia Juana_ [= _1.5 km. SSW Yerbabuena_], 1; _Laguna
Honda_, 1840 m. [= _1.5 km. S Yerbabuena_], 3; 9 mi. SE Taxco, 3800 ft.,
1[22]; _17 km. S Taxco_, 4000 ft., 2[20]; _Iguala_, 5[19]; _3.2 km. SSE
Iguala_, 970 m., 1; 1 km. SSE Texcaizintla, 1600 m., 2; _Teloloapan_,
20[19], 5[24]; _1 km. N Chapa_, 1470 m., 6; _Chapa_, 1470 m., 5; El Limon,
3[18]; 2-1/2 mi. W Mexcala, 2100 ft., 1[20]; _Rio Balsas_, 1[18]; Ayusinaha
[= Ayotzinapa], 1[18]; _Tlapa_, 3900 ft, 1[18]; _2.5 mi. S Almolonga_,
5600 ft., 13[20]; _1 km. N Zihuatanejo_, 1; Zihuatanejo Bay, 4[19]; _Las
Gatas_ [= _2 km. S. Zihuatanejo_], 2; _2 km. SSE Zihuatanejo_, 9; _4 mi.
W Chilpancingo_, 5800 ft., 3[20]; _Chilpancingo_, 4800 ft., 14[18], 21[19],
45[21]; _2 mi. N Tixtla_, 4400 ft., 3[20]; _3.2 km. S Chilpancingo_, 4;
_Cd. Chamilpa_ [= _12 km. ESE Chilpancingo_], 5; _Tlalixtaquilla_, 4200
ft., 2[18]; _15 km. S. Chilpancingo_, 4300 ft., 10[20]; _1 mi. SW
Colotlipa_, 2700 ft., 16[20]; _2 mi. SW Colotlipa_, 2700 ft., 1[20];
_Achuitzotla_, 2800 ft., 7[20]; _8 mi. SW Colotlipa_, 1[20]; _5 mi. S
Rincon_, 2600 ft., 2[20]; _8 mi. SW Tierra Colorado_, 600 ft., 1[20]; Rio
Aguacatillo, _30 km. N Acapulco_, 1000 ft., 3[20]; 5 mi. ESE Tecpan, 50
ft., 9; _Ejido Viejo_, _12 km. NNW Acapulco_, 1; _2 mi. NNW Acapulco_,
7; Acapulco, 3[18], 3[21]; Omentepec, 200 ft., 7[18]. OAXACA: _4 mi. E
Huajuapam_, 5000 ft., 1; 2 mi. NW Tamazulapan, 6550 ft., 1; Yalalag,
3000 ft., 5[18]; _11 mi. NW Oaxaca_ [_City_], 1; _Yaganiza_, 3900 ft.,
1[18]; Oaxaca [City], 5000 ft., 15, 7[21], 7[19], 5[24]; _3 mi. ESE Oaxaca_
[_City_], 30; _4 mi. ESE Oaxaca_ [_City_], 5050 ft., 1; _10 mi. SE
Oaxaca_ [City], 1[22]; _Cerro Ocotepec_, 1[23]; Tepantepec, 9[23]; _1 mi. E
Tlacolula_, 5500 ft., 53[19]; _3 mi. W Mitla_, 11; Jalapa, El Campanario,
1[23]; _2 mi. SE Matalan_, 5950 ft., 14; _Lachiguiri_, 2[23]; _Tres
Cruces_, 10[23]; _Agua Blanca_, 11[23]; _San Jose_, 1[23]; Reforma, 30[19],
7[21], 10[23], 6[24] _Totolapa_, 1[18]; _Nejapa_, _85 km. WNW Tehuantepec_,
500 m., 12[19], 6[24]; _Chicapa_, 2[18]; _Gueladu_ [= _Jalapa_], 6[23];
_Juchitan_, _Laguna Superior_; Manteca, 8[23], 1[23]; San Bartolo, 3000
ft., 1[18]; _Ejutla_, 1400 m., 21[19]; _El Bambita_, _Tequisitlan_ 4[23];
_Mixtequilla_, 2[23]; _Guiencola_, 5[23]; _Tehuantepec_, 200 ft., 26[18],
11[19]; _Sola de la Vega_, 26[19], 3[24]; Huilotepec, 13[18], 3[23]; _Santa
Lucia_, 24[23]; _Cerro de Paste_, _Tenango_, 7[23]; _Sta. C. Quieri_,
3[23]; _Santa Marie Ecatepec_, _Zarzamora_, 13[23]; _Rincon Bamba_, 11[23];
_3 mi. W Miahuatlan_, 5300 ft., 1; _Miahuatlan_, 12[19], 1[23], 6[24]; _San
Juan Acaltepec_, 5[23]; _Zapotitlan_, 1[23]; _Llano Grande_, 3[18];
Pinotepa, 700 ft., 2[18]; Juquila, 8[18]; _Arroyo_, _San Juan_, _north of
Cerro Otate_, 1[23]; Cerro Otate, 3[23]; 3 mi. S Candelaria, 1.
_Marginal records._--MORELOS: 5 mi, W Tepoztlan, 6000 ft. PUEBLA: 2 mi.
S Atlixco, 5800 ft.; Acatlan, 4100 ft. OAXACA: 2 mi. NW Tamazulapan,
6550 ft; Tepantepec; Oaxaca [City], 5000 ft; Yalalag, 3000 ft; Jalapa,
El Campanario; Reforma; Huilotepec; 3 mi. S Candelaria; Cerro Otate;
Pinotepa, 700 ft. GUERRERO: Acapulco; Zihuatanejo Bay; El Limon; 9 mi.
SE Taxco, 3800 ft.
[18] U. S. Nat. Museum (Biol. Surv. Coll.).
[19] Univ. Michigan, Museum of Zoology.
[20] Texas A & M, Cooperative Wildlife Research Collection.
[21] Chicago Natural History Museum.
[22] California Academy of Sciences.
[23] American Museum of Natural History.
[24] University of Florida Collections.
=Baiomys musculus pullus= Packard
_Baiomys musculus pullus_ Packard, Univ. Kansas Publs., Mus. Nat.
Hist., 9:401, December 19, 1958.
_Baiomys musculus grisescens_, Goodwin, Bull. Amer. Mus. Nat. Hist.,
79(2):161, May 29, 1942 (part); Miller and Kellogg, Bull. U. S. Nat.
Mus., 205:513, March 3, 1955 (part); Hall and Kelson, The Mammals of
North America, 2:661, March 31, 1959 (part).
_Type._--Adult female, skin and skull; No. 71605 University of Kansas
Museum of Natural History; 8 mi. S Condega, Esteli, Nicaragua, obtained
on July 15, 1956, by A. A. Alcorn, original number 4218.
_Range._--West-central Nicaragua, from Matagalpa northwest into the
valley of the Rio Esteli, east as far as Jinotega, see Figure 10. Zonal
range: Upper Tropical Life-zone.
_Diagnosis._--Size medium to small for the species; dorsum
Fuscous-Black, individual hairs black-tipped with a subterminal band of
Ochraceous-Buff, Neutral Gray at base; some hairs on dorsum all black to
Neutral Gray at base; hair on sides Neutral Gray tinged with blackish;
face blackish, becoming buffy on sides of head, and white on throat;
vibrissae black; tail unicolored Chaetura Black; forefeet and hind feet
sooty to dusky-white; mid-ventral region of venter white, hairs white to
base; in region of anus and throat, hairs white-tipped, Neutral Gray at
base; average and extreme external and cranial measurements of the type
and 16 paratypes are as follows: total length, 117.3 (111-121); length
of tail vertebrae, 47.2 (44-50); length of body, 70.4 (66-74); length of
hind foot, 15.5 (14-17); length of ear from notch, 11.9 (10-13);
occipitonasal length, 19.3 (18.9-19.8); zygomatic breadth, 10.2
(9.7-10.6); postpalatal length, 7.0 (6.8-7.3); least interorbital
breadth, 3.9 (3.8-4.1); length of incisive foramina, 4.3 (4.0-4.6);
length of rostrum, 7.0 (6.5-7.4); breadth of braincase, 9.6 (9.3-10.0);
depth of cranium, 7.0 (6.8-7.3); alveolar length of maxillary tooth-row,
3.1 (3.0-3.2); for photographs of skull, see Plate 1_h_, and Plate 3_h_.
_Comparisons._--From _B. m. grisescens_, _B. m. pullus_ differs in:
dorsum and tail darker; sides and lateral parts of venter grayish
instead of buffy-brown, thus forming distinct mid-ventral white stripe;
average length of body and tail significantly longer, thus total length
greater; maxillary tooth-row significantly shorter; slightly larger in
other cranial and external dimensions.
From _B. m. nigrescens_, _B. m. pullus_ differs in: dorsum slightly
darker; face grayish, not sooty; mid-ventral white stripe (absent in
most specimens of _nigrescens_) present and becoming grayish laterally;
tail darker, less hairy, and averaging significantly longer; smaller in
most external and cranial dimensions.
_Remarks._--_B. m. pullus_ resembles _B. m. nigrescens_ in size and
color but can readily be distinguished from _nigrescens_ by the shorter
tail. _B. m. pullus_ intergrades with _nigrescens_ as shown by
specimens, referable to _B. m. nigrescens_, from 1 mi. NW San Salvador
and from 1 mi. S Los Planes, El Salvador. In color of the dorsum,
specimens from these localities are intermediate between _nigrescens_
and _pullus_.
The mid-ventral white stripe characteristic of _pullus_ is present in
three of 28 adults from El Salvador. Goodwin (1942:160) reported white
hairs on the pectoral region of several topotypes of _B. m. grisescens_.
The areas of white hairs on the venter of _grisescens_ occur in
approximately 10 per cent of the specimens examined, whereas in
_pullus_, the frequency of occurrence is 90 per cent. The areas of white
hairs in _grisescens_ are in broad patches on the pectoral region, while
in _pullus_, a white stripe passes from the pectoral region to the
inguinal region in both males and females. I know of no selective
advantage that the presence of this white stripe would confer on the
mice.
_Specimens examined._--Total 46, all from NICARAGUA, and distributed as
follows: Type locality, 32 (including the type); _9 mi. NNW Esteli_, 8;
_8 mi. NNW Esteli_, 3; San Rafael Del Norte, 1 (Amer. Mus. Nat. Hist.);
_1 mi. NW Jinotega_, 1; Matagalpa, 1 (Amer. Mus. Nat. Hist.).
_Marginal records._--NICARAGUA: San Rafael Del Norte; Matagalpa; type
locality.
=Baiomys taylori=
Northern Pygmy Mouse
(Synonymy under subspecies)
_Type._--_Hesperomys_ (_Vesperimus_) _taylori_ Thomas, Ann. Mag. Nat.
Hist., Ser. 5, 19:66, January, 1887.
_Range._--Southeastern Arizona and southwestern New Mexico, south into
Chihuahua and Durango, just east of the Sierra Madre Occidental, thence
southeast through Zacatecas, Aquascalientes, Jalisco, Queretaro, and
Guanajuato; two fingerlike projections extend northward, one on the west
along the coast of Sinaloa into southern Sonora, and the other on the
east covering eastern San Luis Potosi, Tamaulipas, eastern Coahuila,
Nuevo Leon, into south, southeast, and north-central Texas. Southern
margin of range in central Mexico approximates the 19th degree of
latitude (see Figure 11). Arid lower and arid upper subdivisions of the
Tropical Life-zone in south; principally Lower Sonoran and Lower Austral
life-zones in north.
_Characters for ready recognition._--Unless otherwise noted, characters
are usable for the age-categories of adult and old adult. Differs from
_B. musculus_ in: hind foot less than 16 millimeters; occipitonasal
length less than 19 millimeters; zygomatic breadth less than 10
millimeters; rostrum deflected ventrally at frontoparietal suture rather
than curving gradually toward anteriormost point of nasals; cingular
ridges and secondary cusps on teeth reduced or absent; basihyal having
entoglossal process much reduced or absent, shoulders of basihyal not
protruding anteriorly, but more flattened (characteristic of all age
categories); baculum having narrower shaft, knob-shaped tip, wings at
base projecting laterally, baculum less than 3 millimeters long; short
process of incus attenuate; muscular process of posterior crus of stapes
reduced.
_Characters of the species._--Size small (extremes in external
measurements of adults: total length, 87-123; length of tail vertebrae,
34-53; length of hind foot, 12-15; length of ear, 9-12). Upper parts
pale drab or reddish-brown to almost black; underparts grayish to
cream-buff.
_Geographic variation._--Eight subspecies are here recognized (see
Figure 11). Features that vary geographically are mostly the same as
those that do so in _B. musculus_ (see page 609).
External and cranial size is less in _B. t. allex_, the southernmost
subspecies, and progressively more in _B. t. paulus_, _B. t. taylori_,
_B. t. ater_, _B. t. subater_, _B. t. fuliginatus_, _B. t. canutus_, and
_B. t. analogous_. Size is largest in subspecies that occur at higher
altitudes. Those subspecies are _B. t. analogous_ and _B. t.
fuliginatus_. The correlation with Bergman's Rule is less exact in _B.
taylori_ than in _B. musculus_. It is noteworthy that the smallest
subspecies, _B. t. allex_, occurs in the area where the two species are
sympatric.
There is close correlation in _B. taylori_, as also in _B. musculus_, of
darker pelages with zones of high relative humidity. The subspecies
having dark pelages are: _analogous_, _fuliginatus_, and _subater_. The
two first-mentioned subspecies occur at high altitudes, and the other,
_subater_, occurs in the humid coastal region of Texas. The paler
subspecies, _taylori_, _canutus_, and _allex_, occur at lower altitudes.
Two subspecies that occur at relatively high altitudes, _ater_ and
_paulus_, are reddish-brown. The color of pelage in these subspecies
resembles the color of soil upon which they live. Blair and Blossom
(1948:5) demonstrated close correlation of color of soil with color of
pelage in _B. t. ater_ by use of an Ives tint photometer.
[Illustration: FIG. 11. Distribution of _Baiomys 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. allex_
2. _B. t. analogous_
3. _B. t. ater_
4. _B. t. canutus_
5. _B. t. fuliginatus_
6. _B. t. paulus_
7. _B. t. subater_
8. _B. t. taylori_]
_Natural History_
_Habitat and numbers._--The habitat occupied by the northern pygmy mouse
ranges from sparse grassy areas along rock walls in central Mexico (see
Davis, 1944:394), and mesquite-cactus associations in southern Texas
(Blair, 1952:242) to heavy stands of grasses such as _Bouteloua_ sp.,
_Andropogon_ sp., _Hilaria_ sp., and sacaton grass intermixed with
_Yucca glauca_ in 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, Queretaro, and Jalisco, _B.
taylori_ is 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 for
_B. taylori_ in 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 Michoacan. Observations of wild-taken _B. taylori_ held 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 captive _B. t. subater_ were much more
tolerant of one another than mice of the genus _Peromyscus_. He pointed
out also that males aided in care of young. In one litter 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, that _B. taylori_ utters
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 of _Microtus_, and often uses runways constructed by
_Sigmodon_. 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 of
_Baiomys_ watch 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 of
_B. taylori_ in 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 of _B. taylori_ consists in part of grass seeds and leaves, prickly
pear (_Opuntia_ sp.) 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 in _B. musculus_), and range from as
few as one to as many as four per litter.
=Baiomys taylori allex= (Osgood)
_Peromyscus allex_ Osgood, 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 Mexico, obtained
on March 7, 1892, by E. W. Nelson, original number 2029.
_Range._--Colima, western lowlands of Michoacan and Jalisco, thence
north into southern half of Nayarit, see Figure 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 Autlan 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, see Plate
1_i_ and Plate 4_a_.
_Comparisons._--For comparisons with _B. t. canutus_, see account of
that subspecies. From _B. t. analogous_, _B. t. allex_ differs 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.
_B. t. allex_ differs from _B. t. paulus_ as 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 of _paulus_ in much the same way as
from _analogous_.
_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 of
_allex_ and those representing _paulus_ and chose to synonomize _allex_
with _paulus_. 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 of
_Baiomys taylori_ (see speciation p. 659). Recently, I (1958b:17-18)
studied ten specimens from Colima (City), Colima, and chose to regard
_Peromyscus [= Baiomys] allex_ as a subspecies. I suggested (_loc.
cit._) that the geographic range of _B. t. allex_ might encompass the
southern part of Nayarit, and western Jalisco. Subsequent study of
specimens from these areas reveals that the populations there are
referable to _allex_. Most of the specimens obtained from these areas,
however, merit special comment.
In color of pelage, those populations from south of the Rio Grande de
Santiago and northwest of Guadalajara (4 mi. SE Ahuacatlan; 1 mi. E
Ixtlan; Etzatlan) show evidence of intergradation with _paulus_ to 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 between _allex_ and _paulus_; from
other localities, some specimens are referable to _allex_, and the
others to _paulus_; from still other localities, all specimens are
referable to _allex_.
A series of 39 specimens from 1 mi. SSE Ameca, 4000 ft., Jalisco, are
uniformly grayish-brown. This series averages grayer than paratypes of
_allex_. There is little, if any, difference between the series from 1
mi. SSE Ameca and paratypes of _allex_ in 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 Michoacan, and at lower elevations in the
west in Jalisco and Nayarit. The means of external and 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 species _B. musculus_ and _B. taylori_ occur together,
interspecific competition seems to have limited, perhaps even reduced,
size of external and cranial parts of _taylori_ (see p. 660).
In color, specimens from the northern part of the valley of the Rio
Tepalcatepec (10 mi. S, 1 mi. W Apatzingan) in Michoacan resemble
paratypes of _allex_. Intergradation probably occurs to the north with
_analogous_.