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  UNIVERSITY OF KANSAS PUBLICATIONS

  MUSEUM OF NATURAL HISTORY


  Volume 9, No. 23, pp. 579-670, 4 pls., 12 figs. in text

  June 16, 1960


  Speciation and Evolution of the
  Pygmy Mice, Genus Baiomys

  BY

  ROBERT L. PACKARD

  UNIVERSITY OF KANSAS
  LAWRENCE
  1960




  UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

  Editors: E. Raymond Hall, Chairman, Henry S. Fitch,

  Robert W. Wilson

  Volume 9, No. 23, pp. 579-670, 4 pls., 12 figs. in text
  Published June 16, 1960


  UNIVERSITY OF KANSAS
  Lawrence, Kansas


  PRINTED IN
  THE STATE PRINTING PLANT
  TOPEKA, KANSAS

  1960

  [Illustration: Look for the Union Label]
  28-3030




Speciation and Evolution of the Pygmy Mice, Genus Baiomys

BY

ROBERT L. PACKARD




CONTENTS


                                                                      PAGE
  Introduction                                                         583
  Materials, Methods and Acknowledgments                               584
  Paleontology of the Genus                                            587
     _Baiomys sawrockensis_                                            588
     _Baiomys rexroadi_                                                589
     _Baiomys kolbi_                                                   590
     _Baiomys brachygnathus_                                           590
     _Baiomys minimus_                                                 591
  Phyletic trends                                                      592
  Non-Geographic Variation                                             595
     Variation with age                                                595
     Secondary sexual variation                                        597
     Individual variation                                              597
     Pelage and molts                                                  598
  Taxonomic Characters and Relationships                               600
     External parts                                                    600
     Pelage                                                            600
     Skull                                                             600
     Teeth                                                             601
     Hyoid apparatus                                                   601
     Baculum                                                           603
     Auditory ossicles                                                 605
  Genus Baiomys                                                        607
  Systematic Accounts of Species and Subspecies                        608
     _Baiomys musculus_                                                608
     _Baiomys musculus brunneus_                                       612
     _Baiomys musculus grisescens_                                     614
     _Baiomys musculus handleyi_                                       617
     _Baiomys musculus infernatis_                                     618
     _Baiomys musculus musculus_                                       620
     _Baiomys musculus nigrescens_                                     623
     _Baiomys musculus pallidus_                                       625
     _Baiomys musculus pullus_                                         628
     _Baiomys taylori_                                                 630
     _Baiomys taylori allex_                                           633
     _Baiomys taylori analogous_                                       637
     _Baiomys taylori ater_                                            640
     _Baiomys taylori canutus_                                         643
     _Baiomys taylori fuliginatus_                                     645
     _Baiomys taylori paulus_                                          647
     _Baiomys taylori subater_                                         650
     _Baiomys taylori taylori_                                         651
  Evolution and Speciation                                             655
     Formation of the Recent Species                                   658
     Areas of present differentiation                                  661
     Zoogeographic position                                            661
  Conclusions                                                          664
  Literature Cited                                                     665




INTRODUCTION


Pygmy mice (_Genus Baiomys_) are the smallest cricetine rodents in North
America. They occur from Nicaragua in Central America into the
southwestern United States. The principal part of the geographic range
of the pygmy mice lies in the Republic of México. They are notably
common in central México, but are only locally common to the north and
to the south, and then only in certain seasons.

Pygmy mice were first brought to the attention of biologists in 1887
when Oldfield Thomas described a diminutive species of cricetine rodent,
_Hesperomys_ (_Vesperimus_) _taylori_. The description was based on a
specimen obtained by William Taylor from San Diego, Duval County, Texas.
C. Hart Merriam (1892:70) described _Sitomys musculus_ on the basis of
specimens from Colima [City of], Colima, México. Merriam (_loc. cit._)
mentioned that the two kinds of mice, _Hesperomys taylori_ and _Sitomys
musculus_, "in general appearance look almost precisely like the common
house mouse (_Mus musculus_) but are still smaller and have shorter
tails." He placed the two species in the genus _Sitomys_. Frederick W.
True in 1894 regarded them as composing a distinct subgenus of _Sitomys,
Baiomys_. According to True (1894:758), _S. taylori_ and _S. musculus_
possessed a different combination of characters (ascending ramus of
mandible short and erect, condyle terminal, coronoid process
well-developed, uncinate, and near the condyle, size small, tail short,
plantar tubercles six, soles hairy) than either _Vesperimus_, or
_Onychomys_ (which had been considered as a subgenus of _Hesperomys_
until 1889). In 1907, E. A. Mearns accorded _Baiomys_ generic rank.
Osgood (1909:252) treated _Baiomys_ us a subgenus of _Peromyscus_,
whereas, Miller, in 1912, regarded _Baiomys_ as a distinct genus. Most
recent students of North American mammals have followed Miller, but
usually with reservations. Ellerman (1941:402) emphasized that the
taxonomic position of the genus was uncertain, and wrote that _Baiomys_
"... seems to be considerably distinct from _Peromyscus_, and may
perhaps be a northern representative of _Hesperomys_ or one of the small
South American genera."

Only two comprehensive analyses of geographic variation and
interspecific taxonomic relationships have been made; the first was by
Osgood (1909) who had fewer than a fourth of the specimens of _Baiomys_
available to me; the second was by Hooper (1952a:90-97) who contributed
importantly to understanding the relationships of the two living species
in central México. No attempts heretofore have been made to correlate
and understand the relationships of the five fossil species to one
another and to the living species assigned to the genus.

Six objectives of the following report are to: (1) list characters
taxonomically useful in recognizing species and subspecies; (2) record
amount of variation within and between populations; (3) correlate
observed variations with known biological principles; (4) show
geographic ranges of the two living species; (5) indicate relationships
between fossil and living species of the genus; and (6) clarify the
systematic position of the genus.




MATERIALS, METHODS AND ACKNOWLEDGMENTS


This report is based on the study of approximately 3,520 museum study
skins, skulls, complete skeletons, and entire animals preserved in
liquid. Most specimens examined were accompanied by an attached label
bearing data on locality and date of capture, name of collector,
external measurements, and sex. In addition, 49 fossil specimens
referable to _Baiomys_ were studied. Nearly two-thirds of the specimens
were assembled at the University of Kansas Museum of Natural History;
the remainder were examined in other institutions.

Specimens studied were grouped by geographic origin, sex, age, and
season of capture. Individual variation was then measured in several of
the larger samples of each living species and in measurable fossil
material. External measurements used were those recorded by the
collectors on the labels attached to the skins. Twenty cranial
measurements employed in the past in the study of _Baiomys_ and closely
related cricetine rodents were statistically analyzed. The coefficient
of variation was calculated for each of the 20 measurements in order to
determine which varied least. In general, measurements having the least
coefficient of variation were used in comparing samples from different
geographic areas. Figure 1 shows the points between which measurements
were taken.

_Occipitonasal length._--From anteriormost projection of nasal bones to
posteriormost projection of supraoccipital bone. _A_ to _A'_

_Zygomatic breadth._--Greatest distance across zygomatic arches of
cranium at right angles to long axis of skull. _B_ to _B'_

_Postpalatal length._--From posterior margin of hard palate to anterior
margin of foramen magnum. _C_ to _C'_

_Least interorbital breadth._--Least distance across top of skull
between orbits. _D_ to _D'_

_Length of incisive foramina._--From anteriormost point to posteriormost
point of incisive foramina. _E_ to _E'_

_Length of rostrum._--The distance in a straight line from the notch
that lies lateral to the lacrimal to the tip of the nasal on the same
side. _F_ to _F'_

_Breadth of braincase._--Greatest distance across braincase, taken at
right angles to long axis of skull. _G_ to _G'_

_Depth of cranium._--The distance from the dorsalmost part of the
braincase to a flat plane touching tips of incisors and ventral border
of each auditory bulla. A glass slide one millimeter thick was placed on
the ventral side of the skull. One jaw of the caliper was on the lower
surface of the slide and the other jaw on the dorsalmost part of the
braincase. The depth of the slide was subtracted from the total reading.
_H_ to _H'_

_Alveolar length of maxillary tooth-row._--From anterior border of
alveolus of M1 to posterior alveolus of M3. _I_ to _I'_

    [Illustration: FIG. 1. Three views of the skull to show points
       between which measurements were taken. Based on _B. m. pullus_,
       adult, female, No. 71611 KU, 8 mi. S Condega, Estelí, Nicaragua.
       × 1-1/3.]

Capitalized color-terms refer to Ridgway (1912). Color terms without
initial letters capitalized do not refer to any one standard.

The names of the cusps and ridges of the teeth (see Figure 2) are those
suggested by Wood and Wilson (1936:389-390). Terminology of the enamel
grooves and folds is that of Hershkovitz (1944:17) and Hooper
(1952b:20-21).

Because secondary sexual variation was not significant (see page 597),
both males and females of like age and pelage were used in comparisons
of samples designed to reveal geographic variation.

The species are arranged from less to more progressive; the subspecies
are arranged alphabetically.

In the synonymy of each subspecies, the plan has been to cite: (1) the
name first proposed; (2) the first usage of the name combination
employed by me; (3) all other name combinations in chronological order
that have been applied to the subspecies concerned.

The localities of specimens examined are listed by country from north to
south. Within a country, the listing is by state, beginning with the
northwesternmost state and proceeding by tiers (west to east) to the
southeasternmost state. Within a state of the United States, the listing
is by counties in the same geographic order as described for states.
Within any county in the United States, within any state in México, and
within any country in Central America, the listing of localities is from
north to south. When more than one locality is on the same line of
latitude, the westernmost locality is listed first. Marginal localities
for each subspecies are listed in a paragraph at the end of each
account. Each marginal locality is mapped by means of a circle. The
circles are listed in clockwise order, beginning with the northernmost.
When more than one of these localities lies on the same line of
latitude, the westernmost is cited first. Localities not represented on
the distribution maps, so as to avoid undue crowding of symbols, are
italicized in the lists of specimens examined.

    [Illustration: FIG. 2. Occlusal views of molars. × 13.

    A.  _B. taylori analogous_, subadult, female, No. 28102 KU, 4 km.
        ENE Tlalmanalco, 2290 meters, Estado de México. Right, upper
        molars.

    B.  _B. musculus musculus_, subadult, male, No. 45456 USNM, Colima,
        Colima, México. Left, upper molars.

    A'. _B. taylori analogous_, subadult, female, No. 28102 KU 4 km.
        ENE Tlalmanalco, 2290 meters, Estado de México. Left, lower
        molars.

    B'. _B. musculus musculus_, subadult, male, No. 45456 USNM, Colima,
        Colima, México. Right, lower molars.]

The largest single collection of pygmy mice is in the University of
Kansas Museum of Natural History, and, unless otherwise indicated,
specimens cited in the taxonomic accounts beyond are there.

I am indebted to the following named institutions and persons for making
specimens available for study:

  American Museum of Natural History, G. G. Goodwin and R. G. VanGelder.

  Carnegie Museum, J. K. Doutt.

  California Academy of Sciences, Robert T. Orr.

  Chicago Natural History Museum, Phillip H. Hershkovitz.

  Cleveland Museum of Natural History (Collection now a part of Museum of
     Zoology, University of Michigan, W. H. Burt, E. T. Hooper).

  Louisiana State University, Museum of Natural History, George H. Lowery,
     Jr.

  Los Angeles County Museum, Charles A. McLaughlin.

  United States National Museum (Biological Survey Collections), David A.
     Johnson, and Viola S. Schantz.

  United States National Museum, Division of Vertebrate Paleontology,
     C. Lewis Gazin.

  University of Arizona, E. L. Cockrum, and G. VR. Bradshaw.

  University of California, Museum of Vertebrate Zoology, Seth B. Benson,
     and W. Z. Lidicker.

  University of Illinois, Museum of Natural History, Donald F.
     Hoffmeister.

  University of Michigan, Museum of Zoology, W. H. Burt, E. T. Hooper, and
     Claude W. Hibbard.

  University of New Mexico, James S. Findley.

  University of Texas, Frank W. Blair.

  Texas A & M, Cooperative Wildlife Research Collection, W. B. Davis.

  The Museum, Michigan State University, Rollin H. Baker.

  University of Florida Collections, James N. Layne.

I am especially grateful to Professor E. Raymond Hall who guided me in
my study and gave critical assistance with the manuscript. Additional
appreciated suggestions were made by Professors A. Byron Leonard, Robert
W. Wilson, Henry S. Fitch, Ronald L. McGregor, and fellow graduate
students. For the illustrations, I am indebted to Mrs. Lorna Cordonnier,
Miss Lucy Remple and Mrs. Connie Spitz. Mr. B. J. Wilks of the
University of Texas, Department of Zoology, provided a number of living
pygmy mice for study in captivity. Mr. J. Raymond Alcorn and his son,
Albert, collected a large share of specimens of pygmy mice now in the
University of Kansas, Museum of Natural History. My wife, Patricia,
aided me in secretarial work and typing of the manuscript.

For financial assistance, I am indebted to the National Science
Foundation when I was a Research Assistant, to the Sigma Xi-RESA
Research Fund for a Grant-in-Aid, and to the Kansas University Endowment
Association through its A. Henley Aid Fund, and the Watkins Fund for
out-of-state field work by the Museum of Natural History.




PALEONTOLOGY OF THE GENUS


Five fossil species, all extinct, have been assigned to the genus and
range in time from early late Pliocene (Saw Rock Canyon fauna of
Hibbard, 1953:408) to Mid-Pleistocene (see Hibbard, 1958:25, who
assigns the Curtis Ranch fauna to late Kansan or early Yarmouth).

I examined all known fossil material and compared it with Recent
material. When the antiquity of the genus is considered, the degree of
difference between the oldest fossil species and the two living species
is much less than might be expected.


=Baiomys sawrockensis= Hibbard

    _Baiomys sawrockensis_ Hibbard, Papers Mich. Acad. Sci., Arts and
       Letters, 38:402, April 27, 1953.

_Type._--No. 27506, Univ. Michigan; left mandibular ramus bearing m1-m3
and incisor; Saw Rock Canyon, early late Pliocene, XI member of the
Rexroad formation, sec. 36, T. 34 S, R. 31 W, Seward County, Kansas
(University of Kansas, Locality 6).

_Referred material._--Univ. Michigan, Nos. 25781, 27503-27505,
28159-28165, 29708-29715, 31015.

_Diagnosis._--Ramus of medium size to small for the genus; lower incisor
broad, moderately recurved; diastemal region broad; anterior median fold
between anterior labial conulid and anterior lingual conulid of m1 deep;
primary first fold between anteroconulid and protoconid of m2 deep;
cingular ridge (ectolophid) at entrance to posteroexternal reëntrant
valley (major fold, see Figure 2) between protoconid and hypoconid of m1
and m2; average and extreme measurements of lower molar row of eight
specimens are, 2.65 (2.5-2.7).

_Comparisons._--For comparisons with _B. brachygnathus_, see account of
that species. From _B. rexroadi_, _B. sawrockensis_ differs in: anterior
median fold of m1 deeper; incisor narrower; diastemal region broader;
coronoid process broader and better developed; cingular ridges
(ectolophids and mesolophids) more pronounced in their development;
incisors less proödont, more retrodont.

From _B. kolbi_, _B. sawrockensis_ differs in: crowns of molars
narrower; incisors less proödont; cingular ridges (ectolophids and
mesolophids) of m1 and m2 more pronounced in their development.

From _B. minimus_, _B. sawrockensis_ differs in: incisor less
procumbent; masseteric ridge extending farther anteriorly; anterior
cingulum of m2 slightly larger.

From _B. musculus_, _B. sawrockensis_ differs in: over-all size of jaw
and molar row less; diastema more acutely curved; incisors shorter;
anterior median fold of m1 slightly deeper.

From _B. taylori_, _B. sawrockensis_ differs in: m1 and m2 smaller;
cingular ridges in m1 and m2 more pronounced; anterolingual conulid
farther forward; incisors shorter, more proödont; molar teeth depressed,
less hypsodont; diastemal region broader, more acutely curved;
masseteric ridge not extending so far anteriorly.

_Remarks._--_B. sawrockensis_ is the oldest known pygmy mouse. The
extreme development of the anterior median fold between the
anterolingual conulid and the anterolabial conulid is regarded as a
primitive feature in the pygmy mice. In this character, the Recent
species can be traced back in time through _B. minimus_ to _B.
sawrockensis_. _B. sawrockensis_ resembles _Calomys laucha_ of South
America in general conformation of jaw and tooth structure. The molars
of _sawrockensis_ are smaller than those of _C. laucha_, and the
anterolingual conulid of _sawrockensis_ is farther forward.


=Baiomys rexroadi= Hibbard

    _Baiomys rexroadi_ Hibbard, Amer. Midland Nat., 26:351, September,
       1941; Hibbard, Contrib. Mus. Paleo., Univ. Michigan, 8(2):145,
       June 29, 1950 (part); Hibbard, Papers Mich. Acad. Sci., Arts
       and Letters, 38:403, April 27, 1953.

_Type._--No. 4670, Univ. Kansas; left mandibular ramus bearing m1-m3,
and incisor; Rexroad fauna, Locality no. 2, Upper Pliocene, Meade
County, Kansas.

_Referred material._--Univ. of Michigan Nos. 24840, 24851, 27493, 27496,
27501, 28862-28867.

_Diagnosis._--Ramus medium in size for the genus; incisors small,
proödont; anterior median fold of m1 slight; cingulum of all molars
poorly developed; average and external measurements of lower molar row
of seven specimens are, 2.7 (2.6-3.0).

_Comparisons._--For comparisons with _B. sawrockensis_ and _B. minimus_,
see accounts of those species. From _B. kolbi_, _B. rexroadi_ differs
in: over-all size of mandibular ramus, incisors, and molars smaller;
anterior median fold of m1 present, though poorly developed.

From _B. brachygnathus_, _B. rexroadi_ differs in: over-all size of
mandibular ramus smaller; m3 larger; posterior cusps (hypoconid and
entoconid) elongated; diastema shorter, less acutely recurved; incisors
less proödont; cingular ridges of m1 and m2 less well-developed.

From _B. musculus_, _B. rexroadi_ differs in: over-all size of
mandibular ramus less; cingular ridges of m1 and m2 less well-developed;
incisors smaller, more proödont; molars less depressed.

From _B. taylori_, _B. rexroadi_ differs in: m3 more triangular,
posterior part narrower; mental foramen closer to anterior root of m1;
masseteric ridge closer to alveolus of m1; incisor shorter, more
proödont; molars more depressed.

_Remarks._--Two maxillary tooth-rows and associated parts were studied.
On one of these specimens, the M2 has a well-developed mesostyle; the
anterior median fold of M1 is also well-developed. The other specimen
possesses a low cingular ridge (enteroloph) between the protocone and
the hypocone, a reduced cingular ridge (mesoloph) between the paracone
and metacone of M1. On the second molar, M2, a mesostyle joins with the
mesoloph somewhat in the fashion indicated by Hooper (1957:9, encircled
number 2).


=Baiomys kolbi= Hibbard

    _Baiomys kolbi_ Hibbard, Trans. Kansas Acad. Sci., 55:201, June 18,
       1952; Hibbard, Papers Mich. Acad. Sci., Arts and Letters, 38:403,
       April 27, 1953.

_Type._--No. 24846, Univ. Michigan; right mandibular ramus bearing m1-m3
and incisor; Fox Canyon, upper Pliocene, Rexroad formation, Rexroad
fauna, Univ. Michigan Locality K1-47, sec. 35, T. 34 S, R. 30 W, XI
Ranch, Meade County, Kansas.

_Referred material._--Univ. Michigan Nos. 24845-24848, 27494, 27497,
27499, 28566, 28861, 28878, 28880-28882, 28884, 28886.

_Diagnosis._--Ramus of medium size to large for the genus; lower incisor
short, narrow transversely, proödont; anterior median fold of m1 reduced
or absent; cingular ridges of m1 and m2 moderately well-developed; m3
large relative to m1 and m2; average and extreme measurements of lower
molars of seven specimens are, 3.0 (3.0-3.1).

_Comparisons._--For comparisons with _B. sawrockensis_ and _B.
rexroadi_, see accounts of those species. From _B. brachygnathus_, _B.
kolbi_ differs in: molar row longer; m3 and jaw larger; diastema longer;
masseteric ridge not so far forward; molars more depressed.

From _B. minimus_, _B. kolbi_ differs in: molar row longer; m3 larger;
jaw larger; diastema not so acutely curved; incisor shorter, narrower
transversely, more proödont.

From _B. musculus_, _B. kolbi_ differs in: anterior median fold of m1
slightly developed or absent, instead of well-developed; m3 larger (not
reduced), external reëntrant valley broad and extending farther across
crown of tooth; incisor smaller, and more proödont; cingular ridges of
m1 and m2 less well-developed.

From _B. taylori_, _B. kolbi_ differs in: molars larger, more depressed;
incisor shorter, more proödont; m3 smaller relative to m1 and m2;
external reëntrant valley of m3 broad, extending farther across crown of
tooth.

_Remarks._--The slight development or absence of the anterior median
fold in _kolbi_ suggests that it was specialized. The anterior median
fold is well-developed in all species of _Baiomys_ save _B.
brachygnathus_ and _B. taylori_, in which the fold is only slightly
developed or absent. _B. kolbi_ may have paralleled _B. taylori_ in
specialization for a diet of grasses and for a life in open country.


=Baiomys brachygnathus= (Gidley)

    _Peromyscus brachygnathus_ Gidley, U. S. Geol. Surv. Prof. Papers,
       131:124, March 15, 1922.

    _Baiomys brachygnathus_, Hibbard, Amer. Midland Nat., 26:352,
       September, 1941.

    _P. [eromyscus] brachygnathus_, Wilson, Carnegie Inst. Washington
       Publ., 473:33, May 21, 1936.

_Type._--No. 10501, U. S. Nat. Mus.; right mandibular ramus bearing
m1-m3, and incisor; 2 mi. NE Curtis Ranch house, near a line between
sec. 28 and 29, T. 18 S, R. 21 E, Mid-Pleistocene (Hibbard, 1958:25),
Cochise County, Arizona.

_Referred material._--None.

_Diagnosis._--Ramus small for the genus; m3 reduced; jaw reduced
anteroposteriorly; incisor short, slender, proödont; cingular ridges
well-developed, posterior ectolophid continuous from protoconid to
hypoconid in m1 and m2; diastema short; length of molar row 2.8 mm.

_Comparisons._--For comparisons with _B. rexroadi_ and _B. kolbi_, see
accounts of those species. From _B. minimus_, _B. brachygnathus_ differs
in: jaw not so slender anteriorly; masseteric ridge not so far anterior;
cheek-teeth slightly broader, less depressed, therefore, more hypsodont;
incisor shorter, more proödont.

From _B. sawrockensis_, _B. brachygnathus_ differs in: molar row
slightly longer; teeth slightly less depressed; masseteric ridge extends
farther anteriorly; incisors more proödont.

From _B. musculus_, _B. brachygnathus_ differs in: jaw smaller; molar
row slightly shorter; molars less depressed; incisors slender, shorter,
narrower, and more proödont.

From _B. taylori_, _B. brachygnathus_ differs in: incisor more slender,
shorter, more proödont; diastema shorter.

_Remarks._--The molar teeth of _B. brachygnathus_, although worn,
resemble those of _B. taylori_ more than those of any known fossil
species. Gidley (1922:124) stated that the absence of the divided
anterior lobe of the first molar (anterior median fold) in
_brachygnathus_ was one of the chief characters separating
_brachygnathus_ from _taylori_. In _taylori_, the anterior median fold
characteristically is only slightly developed, and in some specimens is
absent. _B. brachygnathus_ differs from _taylori_ chiefly in proödont
incisors, which feature seems to preclude _brachygnathus_ being
ancestral to _taylori_. _B. brachygnathus_ may have been a specialized
divergence from _B. minimus_.


=Baiomys minimus= (Gidley)

    _Peromyscus minimus_ Gidley, U. S. Geol. Surv. Prof. Papers,
       131:124, March 15, 1922.

    _Baiomys minimus_, Hibbard, Amer. Midland Nat., 26:352, September,
       1941; Gazin, Prof. U. S. Nat. Mus., 92(3155):488, 1942.

    _P. [eromyscus] minimus_, Wilson, Carnegie Inst. Washington Publ.,
       473:33, May 21, 1936.

_Type._--No. 10500, U. S. Nat. Mus.; left mandibular ramus bearing m1-m3
and incisor; 2 mi. S Benson, sec. 22, T. 17 S, R. 20 E, Late Pliocene
(Blancan, Gazin, 1942:482), Cochise County, Arizona.

_Referred material._--None.

_Diagnosis._--Ramus small for the genus; molar teeth depressed; cingular
ridges (ectolophids) of m1 and m2 well-developed; anterior median fold
present (appearing larger owing to chip of enamel missing); external
reëntrant fold of m3 progresses half way across crown of tooth; diastema
short; incisor moderately large, recurved; length of molar row, 2.6 mm.

_Comparisons._--For comparisons with _B. brachygnathus_, _B. kolbi_, and
_B. sawrockensis_, see accounts of those species. From _B. rexroadi_,
_B. minimus_ differs in: anterior median fold deeper; incisor longer,
more recurved, less proödont; molars slightly more depressed (though
worn).

From _B. musculus_, _B. minimus_ differs in: over-all size of jaw and
molars smaller; incisors shorter; masseteric ridge more depressed.

From _B. taylori_, _B. minimus_ differs in: anterior median fold
slightly deeper; molar teeth more depressed; cingular ridges on m1 and
m2 better developed; masseteric ridge more depressed.

_Remarks._--Gidley (1922:124) stated that _B. minimus_ differed
considerably from _B. taylori_ in that the coronoid portion of the
ascending ramus diverges at a wider angle from the alveolar part of the
jaw. Study of large samples of lower jaws of _B. taylori_ reveals
considerable individual variation in the angle formed between the
coronoid part of the jaw and the alveolar part.

_B. minimus_, except for its small size, is like _B. musculus_ and is
considered to be ancestral to that species.




PHYLETIC TRENDS


It seems that the important trends in phyletic development in the pygmy
mice have been from an ancestral stock (see Figure 3) that possessed
relatively brachydont teeth having raised cingular ridges (ectolophids
and mesolophids) and relatively short orthodont to proödont incisors, to
species having teeth more hypsodont on which cingular ridges were
reduced, stylids were isolated or completely absent, and incisors were
longer and more recurved or retrodont. _Baiomys sawrockensis_, or an
unknown stock resembling it, might have been ancestral to the other
known species. Of the four remaining fossil species, _B. kolbi_ seems
least likely to have been ancestral to the two living species, owing to
its proödont incisors, reduction of cingular ridges, loss of an anterior
median fold in m1, and long mandibular tooth-row. _B. kolbi_ may have
been an early, specialized derivation from the ancestral stock. From his
knowledge of the habitats of _B. musculus_, the larger species, and _B.
taylori_, the smaller species, Hibbard (1952:203) suggests that _B.
kolbi_, a large species, might have inhabited lowlands, and _B.
rexroadi_, a small species, highlands. I have no evidence to dispute
this suggestion except that _B. musculus_ has more prominent cingular
ridges (or at least vestiges of this lophid condition) than either _B.
kolbi_ or _B. rexroadi_. _B. musculus_ (see page 610) is less of an open
grassland inhabitant than is _B. taylori_. Therefore, both _B. kolbi_
and _B. rexroadi_, because of their poorly developed cingular ridges,
might be expected to have lived in a relatively open grassland habitat.

The relationship of _B. rexroadi_ to fossil species other than _B.
kolbi_ is not clear. Superficially, the former resembles _B. taylori_,
but, owing to the specialized development of the molars of _rexroadi_,
it could hardly have been ancestral to either of the living species. The
resemblance of _B. rexroadi_ to _B. taylori_ may result from each having
occupied the same ecological niche in different periods. The incisors of
_B. rexroadi_, however, are much shorter than those of _B. taylori_ and
suggest somewhat different food habits.

_B. minimus_ seemingly is more closely related to _B. sawrockensis_ and
_B. musculus_ than to the other described species. The development of
the cingular ridges leads one to suspect that _B. minimus_ was the
ancestor of _B. musculus_. _B. minimus_ may have been derived from a
_sawrockensis_-like stock and probably gave rise to _B. musculus_.

Hershkovitz (1955:643-644) suggests that "... primitive brachydont,
buno-mesolophodont cricetines have survived ... in forested parts of the
range," whereas "... the progressive branch of cricetines with mesoloph
absent or vestigal, has become increasingly specialized for life in open
country and a diet of grasses." Species of the genus _Baiomys_ can be
divided into two morphological groups. One group, composed of _B.
sawrockensis_, _B. minimus_, and _B. musculus_, includes those species,
the teeth of which were relatively brachydont and had prominently
developed cingular ridges (ectolophids or mesolophids) or, at least,
showed some development of these ridges. _B. sawrockensis_ probably
lived in semi-wooded to shrubby habitats. According to Hibbard
(1953:409), "The Saw Rock Canyon fauna lived in that area at a time when
conditions were comparable to the conditions at the time the Rexroad
fauna lived." The conditions in which the Rexroad fauna lived are
discussed by Hibbard (1941:95). Presumably, there were at least some
well-wooded situations, and the climate was warm. _B. sawrockensis_
probably inhabited denser vegetation than did _B. minimus_ or than does
_B. musculus_. The teeth of the second group (_B. kolbi_, _B. rexroadi_,
_B. brachygnathus_, and _B. taylori_) lack cingular ridges or have them
much reduced and have more hypsodont molars. The three fossil species
probably inhabited relatively open grassland. This assumption is based
largely on the known habitat of _B. taylori_ (see page 632).

The suggested grouping, based on supposed similarities in niches
inhabited by the extinct species, does not necessarily indicate degree
of relationship. _B. taylori_ probably was not derived from an ancestor
like _B. rexroadi_ or _B. kolbi_, although, in certain characters, the
three species resemble one another. _B. kolbi_ and _B. rexroadi_ were
already specialized in Blancan times, probably for living on grassland.
_B. taylori_ shows only a slight advance in specialization of molar
structures compared to either of the aforementioned species but is
slightly smaller and does have longer and more recurved incisors. If
only morphological criteria of lower jaws were considered, without
recourse to other data derived from the study of many samples of
populations of the living species, time alone might account for the
differences among _B. taylori_, _B. rexroadi_, and _B. kolbi_. The
available evidence (see page 658) suggests, however, that _B. taylori_
was derived from the _B. sawrockensis_-_B. minimus_-_B. musculus_ line.

    [Illustration: FIG. 3. Diagram indicating probable relationships
       of living and extinct species of pygmy mice.]

_Baiomys_ seems to have undergone little basic evolutionary and
morphological change since Late Pliocene time. According to Simpson
(1945:207), hesperomine rodents as a group have undergone little basic
evolution, and "The rapid evolution of new genera was more a matter of
segregation of characters in a group with a great variation than of the
origin of significantly new characters." Perhaps, the living southern
pygmy mouse retains many basic characteristics of one of the early North
American cricetine-like stocks that emigrated to South America near the
end of the Pliocene epoch. There is much to suggest close relationship
of the pygmy mice to certain species of South American hesperomine
rodents of the genus _Calomys_.




NON-GEOGRAPHIC VARIATION


Non-geographic variation in pygmy mice (variation in a single population
resulting from age, individual, seasonal, and secondary sexual
differences) has been but little studied in the past. Mearns (1907:381)
figured progressive stages of wear on the teeth of _B. taylori_; Osgood
(1909:252) and Blair (1941:380) referred to changes in dentition,
weights, and pelages.

The largest samples available for this study were 47 _B. taylori_ from
the vicinity of Altamira (6 mi. N, 6 mi. W; 5 mi. N, 5 mi. W; 1 mi. S),
Tamaulipas, and 44 _B. musculus_ from El Salvador (1 mi. S Los Planes,
and 1 mi. NW San Salvador--two localities 3 miles apart).


VARIATION WITH AGE

Specimens of both species were segregated into five categories:
Juveniles, young, subadults, adults, and old adults. Juvenal and young
pygmy mice are readily separable from the other three categories;
subadults are less easily distinguished from adults. In order to obtain
an accurate understanding of geographic variation in these mice, only
adults should be used in making taxonomic comparisons.

_Juveniles._--Nestling mice yet unweaned; sutures in cranium
incompletely closed; bony parts of skull fragile; M3 and m3 not erupted
or only partly erupted and not protruding above margins of alveoli.

At birth, juveniles are pink, without pelage except for the mystacial
vibrissae and a few hairs about the eye. Blair (_op. cit._:381) recorded
changes with age in color of the skin of new-born and suckling pygmy
mice. Data obtained by me from three litters born in captivity agree
with his findings. Pygmy mice are weaned when 17 to 24 days old. At that
time, the mice possess a fine, but not dense, dusky-gray fur.

_Young._--Weaned mice; cranium fragile; sutures between frontals and
parietals, interparietal and parietals, basioccipital and basisphenoid,
basisphenoid and presphenoid, premaxillaries and maxillaries widely
open; M3 and m3 erupted beyond margins of their alveoli (molars erupt
from anterior to posterior; M3 and m3, therefore, are last to erupt); in
some specimens, molars slightly worn; pelage still dusky and relatively
fine and sparse.

_Subadults._--Sutures between bones of skull less widely open than in
young; epiphyses of long bones incompletely coalesced to shaft; relative
to length of skull, braincase higher and rostrum shorter than in adults;
all cusps worn, but dentine not occlusally confluent; primary first and
second folds of third upper molars present; primary first fold and major
fold of lower molars visible; pelage a subtle mixture of colors of young
and adult, but resembling most that of adult; molts into postjuvenal
pelage between 46 and 50 days.

_Adults._--Sutures of skull, and those between epiphyses and shaft of
long bones obliterated except that, in some mice, sutures of skull
persist between frontoparietal, and interparietal; cusps of molars so
worn that dentine occlusally confluent; small island of enamel in third
upper and lower molars of some specimens; relative to length of skull,
cranium lower, rostrum longer, and interorbital region narrower than in
subadult; cranium appears to be more flattened dorsoventrally; between
subadult and adult stages, principal growth occurs in basioccipital,
basisphenoid, frontals, and parietals; nasals grow less.

Although all bones of the skull grow in the subadult and early adult
stages (see table 1), the above-named bones grow faster than others and
thus cause the general flattening of the skull, typical of adults
(similar to that reported by Hoffmeister, 1951:7). The body continues to
lengthen, accounting for the increase in total length of the adult (see
table 1). Hind foot, tail and ear, reach their maximum lengths by
subadult stage. Adult pelage has been acquired, and the color is
brighter than in either subadults or old adults.

_Old Adults._--Characterized principally by well-worn molars; only thin
peripheral band of enamel along with slight evidence of any primary or
secondary folds on any teeth remain; all bones of skull coalesced;
epiphyses and shafts of long bones ankylosed; small bony protuberances
on many skulls; pelage usually ragged, tips of the hairs being worn
away; white flecking and spotting not common, but occurs in some adults.

    TABLE 1.--Average and Extreme Measurements (in Millimeters) of
       Skulls of Five Age-groups of Baiomys taylori from vic.
       (see p. 595) Altamira, Tamaulipas, Mexico.

  =============+===========+===========+===========+===========+===========
  Age groups   | Juvenile  |   Young   | Subadult  |   Adult   | Old adult
  -------------+-----------+-----------+-----------+-----------+-----------
  Number       |           |           |           |           |
  examined     |     3     |     3     |     14    |    19     |    8
               |           |           |           |           |
               |           |           |           |           |
  Total length |   77.0    |   92.6    |    97.6   |   99.9    |  101.6
               |  (74-79)  |  (89-96)  |   (91-103)| (93-105)  | (98-107)
               |           |           |           |           |
               |           |           |           |           |
  Length       |   27.3    |   39.3    |   40.4    |   39.8    |   40.9
  of tail      |  (24-29)  |  (37-41)  |  (36-43)  |  (35-45)  |  (38-45)
               |           |           |           |           |
               |           |           |           |           |
  Length       |   49.6    |   53.3    |   57.0    |   60.0    |   60.7
  of body      |  (49-50)  |  (52-55)  |  (51-61)  |  (56-67)  |  (57-67)
               |           |           |           |           |
               |           |           |           |           |
  Length of    |    11.0   |     13.6  |   14.3    |   14.5    |   14.2
  hind foot    |    (11)   |  (13-14)  |(13.5-15.0)|  (14-15)  |  (13-15)
               |           |           |           |           |
               |           |           |           |           |
  Occipitonasal|   14.2    |    16.3   |   17.1    |   17.7    |   17.8
  length       |(13.6-15.2)|(15.8-16.9)|(16.7-17.6)|(17.2-18.3)|(17.6-18.1)
               |           |           |           |           |
               |           |           |           |           |
  Zygomatic    |    8.1    |    8.7    |    8.9    |    9.3    |    9.4
  breadth      | (7.8-8.6) | (8.6-8.8) | (8.6-9.3) | (9.0-9.6) | (9.1-9.6)
               |           |           |           |           |
               |           |           |           |           |
  Interorbital |    3.4    |    3.4    |    3.4    |    3.6    |    3.5
  breadth      | (3.3-3.5) | (3.3-3.6) | (3.3-3.6) | (3.4-3.8) | (3.3-3.6)
               |           |           |           |           |
               |           |           |           |           |
  Incisive     |           |           |           |           |
  foramina     |     2.9   |    3.5    |    3.7    |    3.9    |    3.9
  (length)     | (2.8-2.9) | (3.4-3.6) | (3.6-3.9) | (3.6-4.1) | (3.5-4.0)
               |           |           |           |           |
               |           |           |           |           |
  Depth        |    5.9    |    6.5    |    6.5    |    6.7    |    6.8
  of cranium   | (5.6-6.2) | (6.3-6.8) | (6.2-6.8) | (6.4-7.0) | (6.5-7.1)
               |           |           |           |           |
               |           |           |           |           |
  Alveolar     |           |           |           |           |
  length,      |    2.7    |    2.9    |    2.9    |    3.0    |    3.0
  upper molars | (2.5-2.8) | (2.9-3.0) | (2.8-3.1) | (2.9-3.2) | (3.0-3.1)
               |           |           |           |           |
               |           |           |           |           |
  Postpalatal  |    4.8    |    5.9    |    6.2    |    6.5    |    6.5
  length       | (4.5-5.3) | (5.8-6.0) | (5.8-6.6) | (6.2-7.2) | (6.3-6.7)
               |           |           |           |           |
               |           |           |           |           |
  Breadth      |    8.1    |    8.5    |    8.4    |    8.6    |   8.6
  of braincase | (7.8-8.7) |   (8.5)   | (8.0-8.7) | (8.3-8.9) |(8.4-8.8)
  -------------+-----------+-----------+-----------+-----------+-----------


SECONDARY SEXUAL VARIATION

The method employed by Dice and Leraas (1936:2) was used to measure the
secondary sexual differences, if there were any, in each of several age
classes. As pointed out by Hooper (1952b:11), individual variation in
small samples can obscure secondary sexual differences. The samples of
_B. taylori_ from the vicinity (see page 595) of Altamira, Tamaulipas,
and the samples of _B. musculus_ from El Salvador (table 2) were large
enough to prevent individual variation from obscuring sexual
differences. Nevertheless, no significant secondary sexual differences
were found in either _B. taylori_ or _B. musculus_ (see table 2).
Therefore, the sexes have been considered together for purposes of
geographic studies.

    TABLE 2.--Analysis of Secondary Sexual Variation in Adult B. taylori
       Vicinity of (see p. 595) Altamira, Tamaulipas, and Adult B.
       musculus from El Salvador (see p. 595). (One Standard Deviation
       on Either Side of the Mean is Given.)

  ==============+==========================+============================
                | Baiomys taylori          | Baiomys musculus
   Character    +------------+-------------+-------------+--------------
                |  21 Males  | 18 Females  |  17 Males   |  13 Females
  --------------+------------+-------------+-------------+--------------
                |            |             |             |
  Total length  |98.4 ± 2.95 |100.5 ± 4.72 |112.04 ± 5.49|113.12 ± 4.23
                |            |             |             |
  Length of tail|40.1 ± 2.31 | 40.3 ± 2.39 | 47.12 ± 2.95| 45.70 ± 2.92
                |            |             |             |
  Length of body|57.83 ± 1.65| 60.10 ± 4.13| 66.67 ± 3.97| 67.75 ± 2.38
                |            |             |             |
  Length of     |            |             |             |
  hind foot     |14.21 ± .53 | 14.44 ± .51 | 15.60 ± .49 | 15.38 ± .64
                |            |             |             |
  Length of ear |10.00 ± .00 | 10.00 ± .00 | 11.80 ± .65 | 12.00 ± .41
                |            |             |             |
  Occipitonasal |            |             |             |
  length        |17.48 ± .40 | 17.47 ± .47 | 19.32 ± .35 | 19.04 ± .44
                |            |             |             |
  Zygomatic     |            |             |             |
  breadth       | 9.17 ± .33 |  9.15 ± .30 |  9.84 ± .21 |  9.91 ± .28
                |            |             |             |
  Least         |            |             |             |
  interorbital  |            |             |             |
  breadth       | 3.53 ± .11 |  3.48 ± .11 |  3.88 ± .08 |  3.88 ± .12
                |            |             |             |
  Postpalatal   |            |             |             |
  length        | 6.35 ± .19 |  6.38 ± .30 |  7.11 ± .15 |  6.95 ± .20
                |            |             |             |
  Depth         |            |             |             |
  of cranium    | 6.65 ± .24 |  6.61 ± .17 |  7.10 ± .18 |  7.08 ± .18
                |            |             |             |
  Incisive      |            |             |             |
  foramina      |            |             |             |
  (length)      | 3.82 ± .15 |  3.81 ± .18 |  4.43 ± .11 |  4.35 ± .14
                |            |             |             |
  Length        |            |             |             |
  of rostrum    | 5.87 ± .20 |  5.88 ± .21 |  6.81 ± .16 |  6.66 ± .31
                |            |             |             |
  Breadth       |            |             |             |
  of braincase  | 8.54 ± .23 |  8.52 ± .12 |  9.84 ± .38 |  9.52 ± .20
                |            |             |             |
  Alveolar      |            |             |             |
  length,       |            |             |             |
  upper molars  | 2.98 ± .08 |  3.01 ± .08 |  3.20 ± .09 |  3.24 ± .10
  --------------+------------+-------------+-------------+--------------


INDIVIDUAL VARIATION

Length of tail varied more than any other measurement used by
me in taxonomic comparisons. Clark (1941:298), Hoffmeister
(1951:16), and Van Gelder (1959:239) point out that external
measurements generally are more variable than measurements of
the cranium, probably because different techniques of measuring
are employed by different collectors. As can be noted in table 3,
females varied more than males.

In the 3520 specimens examined, an extra tooth was observed in
only one (see Hooper, 1955:298). The left mandibular tooth-row
of an adult male (USNM 71539) from Omentepec, Guerrero, is
worn more than the right one. Irregularities in number of teeth
and abnormalities in individual teeth seem to be rare in pygmy
mice.

    TABLE 3.--Individual Variation: Coefficients of Variation for
       Dimensions of External and Cranial Parts in a Population of
       B. Musculus and B. Taylori.

  =====================+=========================+=========================
                       | Baiomys taylori         | Baiomys musculus
                       +-------------------------+-------------------------
                       |   Vic. (see page 595)   |  Vic. (see  page 595)
    Measurement        |   Altamira, Tamaulipas  |      El Salvador
                       +-----------+-------------+------------+------------
                       | 21 Males  | 18 Females  | 17 Males   | 13 Females
                       |   C. V.   |    C. V.    |   C. V.    |    C. V.
  ---------------------+-----------+-------------+------------+------------
                       |           |             |            |
  Total length         |    3.0    |     4.7     |   4.9      |    3.7
  Length of tail       |    5.7    |     5.9     |   6.2      |    6.4
  Length of body       |    2.8    |     5.0     |   5.9      |    3.5
  Length of hind foot  |    3.7    |     3.4     |   3.0      |    4.1
  Length of ear        |    0.0    |     0.0     |   5.5      |    3.3
                       |           |             |            |
  Occipitonasal length |    2.2    |     2.7     |   1.8      |    2.3
  Zygomatic breadth    |    3.6    |     3.3     |   2.2      |    2.7
  Interorbital breadth |    3.2    |     3.3     |   2.2      |    2.9
  Incisive foramina    |           |             |            |
    (length)           |    3.8    |     4.6     |   2.5      |    3.2
  Depth of cranium     |    3.6    |     2.5     |   2.5      |    2.5
  Alveolar length,     |           |             |            |
    upper molars       |    2.7    |     2.5     |   2.8      |    3.2
  Postpalatal length   |    3.1    |     4.7     |   2.1      |    2.9
  Length of rostrum    |    3.3    |     3.6     |   2.4      |    4.7
  Breadth of braincase |    2.7    |     1.4     |   4.0      |    4.9
  ---------------------+-----------+-------------+------------+------------

The posterior margin of the bony palate varies from semicircular to
nearly V-shaped. The suture between the nasals and frontals varies from
V-shaped to truncate to W-shaped. The maxillary part of the zygoma
varies from broad to slender in dorsoventral width in both species.


PELAGE AND MOLTS

There are three distinct pelages, juvenal, postjuvenal, and adult. The
sequences of molt and change of pelage from the juvenal, to the
postjuvenal, and from it to adult, are essentially as reported for
_Peromyscus_ by Collins (1918:78-81; 1924:58-60) and Hoffmeister
(1951:5). The juvenal pelage is uniformly dusky gray throughout except
for the paler gray on the venter. In most juvenal mice, the yellow to
ochraceous pigments of the subterminal bands are reduced or absent.
Unlike _Peromyscus_, _Baiomys_ has bright brownish hairs on the head as
the first evidence of the postjuvenal molt (see Figure 4, part a). Blair
(1941:381) reports adult pelage in pygmy mice being evident first at an
age of 46 days. Two of my juveniles born in captivity began the
postjuvenal molt on the 38th and 40th days. The area of new hairs on the
head spreads most rapidly posteriorly. New hair appears ventrally and
laterally at the end of 46 days (see Figure 4, part b). Hair replacement
proceeds more slowly after the "saddle back" stage (described in
_Peromyscus_ by Collins, 1918:80) has been reached. That stage was
reached in two pygmy mice at 52 days (see Figure 4, part c). Areas
immediately posterior to the ears, in the scapular region, molt last.
The postjuvenal pelage was seemingly complete in one captive pygmy mouse
at the end of 60 days. Another captive failed to complete its growth of
new pelage until two additional weeks had elapsed. Length of time
required to molt in pygmy mice is about the same as that reported by
Layne (1959:72) in _Reithrodontomys_.

    [Illustration: FIG. 4. Diagrams showing progress of the postjuvenal
       molt in pygmy mice. For explanation of a, b, and c, see text.
       All approximately 2/3 natural size.]

If, after the postjuvenal molt, a distinct adult pelage is acquired it
is difficult to separate it from the annual replacement of pelage in
adults at the beginning of the rainy season. Adults of both species have
been found in molt in all months of the year. To the north, in Texas,
the pelage of winter-taken specimens is denser and slightly more reddish
than that of specimens taken in spring and summer. In the two last
mentioned seasons, the pelage is more uniformly gray. To the south, in
México, the pelage is heavy and long in most specimens taken in the
rainy season. The percentage of specimens in molt immediately before the
rainy season and immediately before the dry season is slightly higher
than in specimens taken at other times of the year. The adult or
seasonal molt (both loss of old pelage and growth of new) resembles that
in _Peromyscus truei gilberti_, described by Hoffmeister (1951:6) as
proceeding "posteriorly as a wave over the entire back." The new hair is
slightly brighter than the old. Old adults are usually in ragged pelage
regardless of season; possibly only one regular annual change of pelage
occurs in most animals before they die. Only one case of melanism was
observed among all the specimens of both species examined. It was a
young male _B. t. taylori_, KU 35943, from 6 mi. SW San Gerónimo,
Coahuila, possessing black hairs throughout. Its hairs are longer and
finer than those on specimens of comparable age and sex. No albino was
found, although Stickel and Stickel (1949:145) record one--an adult male
of _B. taylori_.




TAXONOMIC CHARACTERS AND RELATIONSHIPS


_External parts._--Length of body, foot, ear, and tail are useful when
considered together in distinguishing species and subspecies. I found as
Hooper (1952a:91) did that length of ear in combination with length of
hind foot suffices to identify nearly all specimens to species,
especially where the two species occur together.

_Pelage._--Color in adults is of especial value in subspecific
determination; the manner in which it varies geographically is described
on pages 609, 630.

_Skull._--Difference in occipitonasal length and zygomatic breadth, both
having low coefficients of variation, are useful in separating species,
especially where they are sympatric. Shape of presphenoid, nasals,
interparietal, frontoparietal sutures, and length and degree of the
openings of the incisive foramina are useful in delimiting subspecies.
The rostrum of _B. taylori_, in front of the frontonasal suture, is
deflected three to five degrees ventrally in 85 per cent of the adults
examined, and in _B. musculus_ is less, or not at all, deflected.

_Teeth._--Alveolar length of the upper and lower molar tooth-rows aids
in distinguishing fossil and Recent species, and to a lesser degree in
delimiting subspecies. Occlusal pattern is useful in estimating the
relationship of fossil and living species. Degree of development of the
mesostyle, mesostylid, mesoloph, and mesolophid have been useful in
determining relationship between fossil and living species as well as
useful in separating the living species. Rinker (1954:119) and Hooper
(1957:48) have shown the degree of variation in dental patterns in
_Peromyscus_, _Sigmodon_, and _Oryzomys_, mice thought to be closely
related to _Baiomys_. In pygmy mice, however, the dental patterns are
relatively constant. The lophs and styles are subject to some geographic
variation but, nevertheless, are useful in estimating relationships.

    [Illustration: FIG. 5. Ventral view of hyoid bones. × 18.

    A. _Baiomys musculus brunneus_, adult, female, No. 30182 KU,
       Potrero Viejo, 1700 feet, Veracruz.

    B. _Baiomys taylori analogous_, adult, female, No. 36761 KU,
       2 mi. N Ciudad Guzmán, 5000 feet, Jalisco.]

_Hyoid apparatus._--Shape and, to a lesser extent, size of the hyoid
apparatus differentiate nearly all specimens of _B. taylori_ from all
those of _B. musculus_. The hyoid of _B. taylori_ differs from that of
_B. musculus_ principally in the shape of the basihyal. It possesses an
anteriorly pointed entoglossal process in _B. musculus_, and is not
rounded to completely absent as in _B. taylori_ (see Figure 5). The
shoulders of the basihyal protrude anteriorly in _B. musculus_, and are
not flattened as in _B. taylori_. The total length was measured in a
sample of 55 basihyals of _B. musculus_, and was compared to the total
length of a sample of 80 basihyals of _B. taylori_. The means of the two
samples differ significantly at the 95 per cent level; the mean plus two
standard errors of _B. musculus_ and _B. taylori_, are, respectively,
2.43 ± .02; 2.18 ± .03. There is sufficient overlap of the samples
(mean plus one standard deviation of _B. musculus_ and _B. taylori_,
respectively: 2.43 ± .15; 2.18 ± .15) to make the total length of the
basihyal of only secondary importance in distinguishing species, but
shape and total length of the basihyal, when considered together, serve
to identify all specimens to species. When length of the basihyal is
plotted against occipitonasal length (see Figure 6), all specimens
studied, regardless of age or geographical origin, were separated at the
level of species. The hypohyals of _B. taylori_ seemingly remain
distinct throughout life; those of _B. musculus_ completely fuse in some
adults. The ceratohyals are highly variable in shape and of little
taxonomic use.

    [Illustration: FIG. 6. Relationship of length of basihyal to
       occipitonasal length of skull. Black symbols, all below the curved
       line, represent measurements of _B. taylori_; open symbols, all
       above the curved line, represent measurements of _B. musculus_.]

The degree of geographic variation in shape of basihyal is not great.
Specimens of _B. musculus pallidus_ from 1 km. NW Chapa, Guerrero, have
a small indentation on the anteriormost part of the entoglossal process.
The shoulder of the basihyal is directed less forward in specimens of
_B. taylori taylori_ from 6 mi. N, 6 mi. W Altamira, Tamaulipas, than in
other specimens of the species. The variations observed seemed not to be
clinal.

According to White (1953:548) the hyoid, like the baculum (Burt,
1936:146), is little influenced by changes in external environment and
may serve to clarify intergeneric relationships. Hyoids of both species
of _Baiomys_ are smaller than hyoids of all subgenera of _Peromyscus_.
In shape, the hyoids of _Baiomys_ resemble those of _Ochrotomys
nuttalli_ (as explained on page 605, _Ochrotomys_ is here accorded
generic, instead of subgeneric, rank). In size, the hyoid of both
species of _Baiomys_ resembles that in _Reithrodontomys_. Sprague
(1941:304) reports a resemblance in shape between the ceratohyals of
_Baiomys_ and _Reithrodontomys_. The thyrohyals differ from those of
_Reithrodontomys_, being less boot-shaped, and having a slight terminal
expansion as in _Ochrotomys_ (see Sprague, _loc. cit._). In shape, the
large basihyal of _Onychomys_ resembles the smaller one of _B.
musculus_. The basihyal of _Oryzomys_ lacks the entoglossal process
present in _Baiomys_. On the basis of shape of hyoid, _Baiomys_ seems to
be most closely related to _Ochrotomys_.

    [Illustration: FIG. 7. Dorsal view of bacula. × 16.

    A. _B. musculus brunneus_, adult, No. 24336 KU, 3 kms.
       W Boca del Río, 10 feet, Veracruz.

    B. _B. taylori taylori_, adult, No. 35937 KU, 6 mi.
       SW San Gerónimo, Coahuila.]

_Baculum._--Of _Baiomys_, 166 bacula were processed, using the method of
White (1951:125), and studied. They provide characters of taxonomic
worth at the level of species and aid in evaluating generic
relationships.

The baculum of _B. taylori_ differs from that of _B. musculus_ in: shaft
narrow; wings anterior to base projecting dorsolaterally instead of
anteriorly; anterior part knob-shaped having indentation at tip, instead
of anterior part spatulate-shaped (in some) to knob-shaped (see Figure
7), without indentation; significantly shorter (see Table 4).

    TABLE 4.--Length of Bacula

  ==============+===========+=========+==========+===========+==========
                | Number of | Average |   3 ×    |    1      |
     Species    | specimens | length  | standard | standard  | Range
                |           |         |  error   | deviation |
  --------------+-----------+---------+----------+-----------+----------
  _B. taylori_  |      108  |  2.535  |   .078   |    .274   | 2.00-3.12
                |           |         |          |           |
  _B. musculus_ |       58  |  3.324  |   .090   |    .233   | 2.80-3.88
  --------------+-----------+---------+----------+-----------+----------

In each of the two species, individual and geographic variation in the
baculum is slight; its length varies insignificantly according to age.
Excluding juveniles contained in Table 4, but including young and
subadults, only three bacula of _B. taylori_ were longer than 3 mm., and
only one baculum of _B. musculus_ (a young) was shorter than 3 mm. The
total length of the baculum, considered together with its shape, serves
to identify to species all specimens examined by me.

The bacula of both species of _Baiomys_ were compared with bacula of
_Akodon_, _Scotinomys_, _Holochilus_, _Oryzomys_, _Zygodontomys_,
_Reithrodontomys_, _Thaptomys_, and _Calomys_ and illustrations of
bacula by Blair (1942:197, 200) of _Peromyscus_ (subgenera _Peromyscus_,
_Haplomylomys_, _Podomys_), _Ochrotomys_, and material at the University
of Kansas Museum of Natural History of _Megadontomys_. Shape of baculum
most resembled that of _Ochrotomys_ and _Calomys_. The bacula of
_Baiomys_, as pointed out by Blair (_op cit._:203), differ as much from
those of the genus _Peromyscus_ as do the bacula of _Reithrodontomys_
and _Onychomys_. In size of baculum, _Baiomys_ resembles _Ochrotomys_.
Blair (_op. cit._:202) pointed out that the length of the baculum of _B.
taylori subater_ was contained in the length of the animal's body 20.3
times, and 24.2 times in the length of that of _Ochrotomys nuttalli_.
The length of the baculum of _B. musculus_ (average of 58 specimens
without regard to subspecies) is contained in the length of the body (of
specimens from which the bacula were removed) 22.7 times, a figure
approaching that in _Ochrotomys_. When bacula of both species of
_Baiomys_ were compared to those of _O. nuttalli_, bacula of _B.
musculus_ were found to most closely resemble those of _O. nuttalli_.
The baculum of a single specimen of _Calomys_ (_C. laucha_) was
contained in the length of the body 15.5 times. In general shape, as
well as in possession of an anterior knob and the position of the
expanded posterior wings, the baculum of _C. laucha_ resembles the
baculum of _Ochrotomys_ and _Baiomys musculus_.

Blair (_op. cit._:201) considers generic _versus_ subgeneric rank for
_Ochrotomys_, and on the basis of studies of the phallus Hooper
(1958:23) stated that "it is clear that _nuttalli_ should be removed
from _Peromyscus_ and should be listed as _Ochrotomys nuttalli_
(Harlan)." I agree with Hooper (_loc. cit._) and point out that on the
basis of the baculum, there is less of a hiatus between _Baiomys_ on the
one hand, and _Ochrotomys_ and _Calomys_ on the other hand, than there
is between any one of those three genera and _Peromyscus_.

White (1953:631) reported that the baculum of chipmunks might indicate
relationships more clearly than do skulls and skins. He thought that
skulls might more quickly than bacula reflect the habitus of the animal.
The resemblance in cranial morphology between _Peromyscus_ and _Baiomys_
is judged to be the result of such a convergence of habitus and the
baculum in _Baiomys_ is thought to reflect relationships more accurately
than does the skull.

_Auditory ossicles._--Examination of a number of auditory ossicles of
_Baiomys_ reveals constant interspecific differences in the malleus and
incus. There is only slight individual variation, slight variation with
age, and no secondary sexual variation. In _Baiomys taylori_ the
orbicular apophysis of the malleus (see Figure 8, A) is rounded to
nearly ovoid; the anterior process is pointed, and the neck is short,
being slightly recurved. The body of the incus is round and the short
process is elongate. The sides of the long limb of the incus are nearly
parallel. The lenticular process is relatively large. The posterior and
anterior crus of the stapes are bowed, and the muscular process is
either absent or much reduced.

In _Baiomys musculus_, the orbicular apophysis of the malleus (see
Figure 8, B) is round to oblong, and less ovoid than in _B. taylori_;
the anterior process is less acutely pointed than in _B. taylori_, and
the neck is long, less recurved than in _B. taylori_. The body of the
incus, though tending to be round, is more flattened, and the short
process is knob-shaped, not elongated. The sides of the long limb of the
incus are not parallel. The lenticular process is, relative to the size
of the incus, small. The posterior and anterior crus of the stapes are
more nearly straight than in _taylori_. A prominent muscular process
occurs on the posterior crus.

The auditory ossicles of representative species of all the subgenera of
_Peromyscus_ were studied as were the ossicles of _Onychomys_,
_Ochrotomys_, _Oryzomys_, _Akodon_, _Thaptomys_, _Zygodontomys_,
_Calomys_, _Reithrodontomys_, and _Holochilus_.

    [Illustration: FIG. 8. Lateral views of auditory ossicles. × 20.

    A. _B. taylori analogous_, adult, female, No. 28104 KU, 4 kms.
       ENE Tlalmanalco, 2290 meters, Estado de México.

    B. _B. musculus pallidus_, adult, male, No. 28346 KU, Cahuilotal,
       Sacacoyuca, 960 meters, Guerrero.]

The general plan of structure of the auditory ossicles in _Baiomys_
resembles that in _Calomys_, _Akodon_, and _Thaptomys_. The ossicles of
_Calomys_ and _Thaptomys_, in particular, closely resemble the auditory
ossicles of _Baiomys musculus_. The short process of the incus is
knoblike in _Calomys_ and _Thaptomys_, and the general conformation of
malleus and stapes in those two genera is nearly identical to that in
_B. musculus_. In _Akodon_, the anterior and posterior crus of the
stapes is more rounded than in _B. musculus_, resembling that in _B.
taylori_.

_Reithrodontomys_ differ from _Baiomys_ in having a more elongate
orbicular apophysis on the body of the malleus, an elongated short limb
on the incus, and a stapes having anterior and posterior crura bowed as
in mice of the genus _Peromyscus_.

In _Ochrotomys_, the orbicular apophysis of the malleus resembles the
orbicular apophysis of _B. musculus_, but the short process of the incus
is longer, resembling the short process of _B. taylori_. In general
conformation of the malleus, incus, and stapes, _Ochrotomys_ shows
closer resemblance to _B. taylori_ than to _B. musculus_.

In _Holochilus_ the anterior crus and posterior crus of the stapes are
similar to those in _B. musculus_, but in shape and size of malleus and
incus, _Holochilus_ differs considerably from _B. musculus_ and _B.
taylori_.

In _Zygodontomys_, size and shape of the ossicles differ greatly from
those of _Baiomys_.

In the genus _Peromyscus_, only _Peromyscus floridanus_ (subgenus
_Podomys_) possesses a knoblike short process on the incus similar to
that in _B. musculus_; representatives of the other subgenera examined
possess an elongated short limb on the incus. The conformation of the
ossicles of both _Onychomys_ and _Oryzomys_ appears to be more nearly
like that in _Peromyscus_ than that of _Baiomys_.

On the basis of shape and size of auditory ossicles, _Baiomys_ resembles
South American hesperomines (_Calomys_ and _Thaptomys_) rather than
North American hesperomines.




Genus =Baiomys= True


    1894. _Baiomys_ True, Proc. U. S. Nat. Mus., 16:758, February 7.
       Type, _Hesperomys (Vesperimus) taylori_ Thomas.

_Diagnosis._--Size small (total length in adults, 93-135); tail shorter
than head and body; hind foot in adults 12-17; ears small (8-12) and
rounded; upper parts blackish sepia to ochraceous-buff; underparts slaty
gray to white or pale buffy; eyes small; hind feet having six plantar
pads, soles nearly naked except for some hairs on anterior parts of
soles and anteriorly to base of toes and between toes; occipitonasal
length of skull in adults, 17.0-21.5; zygomatic breadth, 9.0-11.5;
coronoid process of mandible well developed, strongly recurved;
ascending ramus of mandible short and erect; anterior palatine foramina
(incisive foramina) long, usually terminating posterior to plane of the
front of first molars; posterior palatine foramina nearly opposite
middle of M2; interorbital space wide relative to widest part of
frontals; nasals projecting only slightly over incisors; condyle
terminal; upper incisors relatively heavy; primary first fold of M3
obliterated at an early stage of wear; major cusps of upper and lower
anteriormost two molars alternating, more so in m1-m2 than in M1-M2,
dental formula I/i, 1/1; C/c, 0/0; P/p, M/m, 3/3 = 16.

For distribution of the genus, see Figure 9.

    [Illustration: FIG. 9. Geographic distribution of the genus
       _Baiomys_. Black area shows where the two species occur together.
       Black dot (Acultzingo, Veracruz) shows locality where _Baiomys
       taylori_ occurs within the range of _B. musculus_, but _B. musculus_
       is not known to occur at that locality.]




SYSTEMATIC ACCOUNT OF SPECIES AND SUBSPECIES


=Baiomys musculus=

Southern Pygmy Mouse

(Synonymy under subspecies)

    _Type._--_Sitomys musculus_ Merriam, Proc. Biol. Soc. Washington,
       7:170, September 29, 1892.

_Range._--Southern Nayarit, Michoacán, México, Morelos, Puebla, and
central Veracruz, southeastward to western Nicaragua, but unknown from
southern Veracruz, Tabasco, and the Yucatán Peninsula (see Figure 10);
occurs principally in the arid upper and lower divisions of the Tropical
Life-zone.

_Characters for ready recognition._--Unless otherwise noted, characters
are usable only for the two age-categories of adult and old adult.
Differs from _B. taylori_ in: hind foot 16 millimeters or more;
occipitonasal length, 19 millimeters or more; zygomatic breadth, 10
millimeters or more; rostrum not deflected ventrally at frontoparietal
suture but, instead, curving gradually toward anteriormost point of
nasals; cingular ridges and secondary cusps on teeth more pronounced;
basihyal having anterior pointed entoglossal process, shoulders of
basihyal protruding anteriorly (characteristic of all age categories);
baculum having broader shaft, spatulate to knob-shaped tip, wings at
base projecting anteriorly; baculum more than 3 millimeters long; short
process of incus knob-shaped rather than attenuate; muscular process of
posterior crus of stapes prominent.

_Characters of the species._--Size large (extremes in external
measurements of adults; total length, 100-135; length of tail vertebrae,
33-56; length of hind foot, 14.1-17; length of ear, 9-12); upper parts
dark reddish brown, or ochraceous-buff to nearly black; underparts pale
pinkish buff to white or pale buffy.

_Geographic variation._--Eight subspecies are here recognized (see
Figure 10). Features that vary geographically are external size, color
of pelage, certain cranial dimensions (occipitonasal length, zygomatic
breadth, least interorbital breadth, length of rostrum, length of
incisive foramina, depth and breadth of cranium, and alveolar length of
upper molar tooth-row).

External and cranial size (except for _B. m. handleyi_) is less in the
southernmost subspecies, _B. m. pullus_, _B. m. grisescens_, _B. m.
nigrescens_, and more in the northernmost subspecies, _B. m. musculus_,
_B. m. brunneus_, and _B. m. infernatis_. Increase in size from south to
north is in keeping with Bergman's Rule that within a species, smaller
individuals occur in warmer parts of its geographic range. Southern
pygmy mice at high altitudes average larger than those from low
elevations, except where the two species are sympatric. There the
Southern Pygmy Mouse is uniformly larger, regardless of altitude.

Osgood (1909:257, 259) suggested that degree of relative humidity might
in some way control color of pelage in both _B. taylori_ and _B.
musculus_. In _B. musculus_, the darker subspecies, _B. m. brunneus_,
_B. m. nigrescens_, and _B. m. pullus_, occur in zones of rather
constant high relative humidity, whereas the paler subspecies
_infernatis_, _musculus_, _handleyi_, and to a less extent _grisescens_
and _pallidus_, occur in zones of lower relative humidity. This is in
keeping with Gloger's Rule, which states that melanins increase in the
warm and humid parts of the range of a species, and reddish or
yellowish-brown phaeomelanins prevail in arid climates. _B. m. musculus_
ranges into areas where relative humidity is such that darker pelages
might be expected, but this is in the area where the two species are
sympatric, and color of pelage may be an important character of
recognition.

    [Illustration: FIG. 10. Distribution of _Baiomys musculus_. Known
       localities of occurrence are represented by circles and black dots;
       the former denote localities that are peripheral (marginal) for the
       subspecies concerned.

    1. _B. m. brunneus_
    2. _B. m. grisescens_
    3. _B. m. handleyi_
    4. _B. m. infernatis_
    5. _B. m. musculus_
    6. _B. m. nigrescens_
    7. _B. m. pallidus_
    8. _B. m. pullus_]

_Natural History_

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

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

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

_Enemies and food._--Owl pellets (thought to be those of a barn owl,
_Tyto alba_) from within the geographic range of _B. musculus_, from 6
mi. SW Izucár de Matemores, yielded mandibular tooth-rows belonging to
_musculus_. Presumably, most of the carnivorous mammals and raptorial
birds within the range of the southern pygmy mouse could be listed as
enemies. Diurnal to crepuscular habits of this mouse may protect it from
some of the nocturnal carnivorous mammals and raptorial birds.

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

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


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

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

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

    [_Peromyscus musculus_] _brunneus_, Elliott, Field Columb. Mus.
       Publ., 95(4): 176, 1904.

    _Peromyscus musculus_ [_musculus_], Osgood, N. Amer. Fauna, 28:258,
       April 17, 1909 (part).

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

    _B._ [_aiomys_] _m._ [_usculus_] _brunneus_, Hooper, Jour. Mamm.,
       33:96, February 18, 1952.

    _Baiomys taylori_, Hooper, Jour. Mamm., 33:97, February 18, 1952
       (part).

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

_Range._--Central Veracruz, coastal plains and eastern slopes of the
plateau of Central México, see Figure 10. Zonal range: Upper Tropical
Life-zone (Lowery and Dalquest, 1951:537), parts of the Veracruz and
eastern Transverse Volcanic biotic provinces of Goldman and Moore
(1945:349). Occurs from near sea level at Boca del Río, Veracruz, up to
5500 feet 3 km. SE Orizaba.

_Diagnosis._--Size medium to large for the species; ground color of
dorsum of paratypes near Olive Brown; darkest of specimens of this
subspecies examined (from Potrero Viejo, Veracruz) between Prouts Brown
and Mummy Brown; distal two-thirds of guard hairs of dorsum black,
proximal third dark gray to sooty; hairs of dorsum black-tipped having
subterminal band of Ochraceous-Tawny; sides paler (less of dark brown)
than dorsum; venter Deep Olive Buff to clay color, individual hairs pale
olive buff at tips, dark gray basally; region of throat and chin sooty
gray; ventralmost vibrissae white to base, other vibrissae black to
base; ears dark brown, sparsely haired; forefeet and hind feet
flesh-colored in palest specimens, sooty in darkest; tail pale brown,
slightly paler below than above; presphenoid only slightly constricted
towards midline; average and extreme external and cranial measurements
of 10 adults from Cerro Gordo, Veracruz, are as follows: total length,
118.9 (112-127); length of tail vertebrae, 45.1 (42-50); length of body,
74.0 (69-78); length of hind foot, 16.0 (16); length of ear from notch,
12.8 (12-13); occipitonasal length, 19.5 (19.0-20.0); zygomatic breadth,
10.3 (10.0-10.8); postpalatal length, 7.1 (6.7-7.5); least interorbital
breadth, 3.9 (3.7-4.0); length of incisive foramina, 4.4 (4.1-4.6);
length of rostrum, 6.9 (6.5-7.2); breadth of braincase, 9.5 (9.2-9.7);
depth of cranium, 7.1 (7.1-7.4); alveolar length of maxillary tooth-row,
3.3 (3.2-3.3); for photographs of skull, see Plate 1_a_, and Plate 3_a_.

_Comparisons._--For comparisons with _B. m. nigrescens_, see account of
that subspecies. From _B. m. pallidus_, _B. m. brunneus_ differs in:
dorsal, lateral, and facial coloration deeper reddish brown, more
melanins present; venter darker; buff gray rather than whitish buff to
gray as in paratypical series; vibrissae black rather than brownish to
white; tail sooty, less flesh-colored; forefeet and hind feet averaging
slightly grayer; most external and cranial dimensions averaging slightly
larger; nasals less attenuated; presphenoid less hour-glass shaped,
sides more nearly straight.

From _B. m. infernatis_, _B. m. brunneus_ differs in: side of face and
neck deep reddish-brown rather than yellowish-gray (the differences in
dorsal colorations are greater between _brunneus_ and _infernatis_ than
between _brunneus_ and _pallidus_); venter darker buff-gray; tail
brownish rather than flesh-colored; forefeet and hind feet average
slightly grayer; most external dimensions averaging slightly larger;
cranial dimensions nearly the same except length of incisive foramina,
which is smaller; presphenoid differs in much the same way as from
pallidus.

_Remarks_.--Specimens from Chichicaxtle, Puente Nacional, 3 km. W Boca
del Río, 1 km. E. Mecayucan, and Río Blanco (20 km. WNW Piedras Negras),
are all paler than the paratypical series and other specimens from
within the assigned range of _B. m. brunneus_. All these specimens from
the coastal plain average considerably paler than those from the front
range and slopes of the mountains. Specimens from Puente Nacional are
intermediate in color between paler, grayish brown, specimens from the
coastal plains and the darker, brown, specimens from the mountains. When
Allen and Chapman (1897:203) described _brunneus_, they did so on the
basis of the darker brown mice from the higher altitudes. The name,
_brunneus_, _sensu stricto_, could be restricted to those mice from the
higher altitudes of central Veracruz. However, when the mice of
intermediate color from Puente Nacional are considered, it seems best to
include the material from the coastal plain with _brunneus_. Crania from
the higher altitudes are slightly larger than, but not significantly
different from, crania of specimens from the coastal plains. Specimens
examined from the coastal plains resemble the darker series of _B. m.
pallidus_ to the west in central México. But there is no evidence of
gene flow between the paler coastal specimens and _B. m. pallidus_ to
the west. In fact, these paler brown mice on the coastal plain grade in
color into the darker brown mice from the mountains. The paler mice from
the coast may be an incipient subspecies.

The type and paratypes seem to have faded somewhat since they were
described by Allen and Chapman (_loc. cit._) and by Osgood (1909:259).
However, the color of the paratypes and other specimens herein assigned
is the feature most useful for distinguishing _brunneus_ from all other
subspecies of _B. musculus_.

_Specimens examined._--Total 187 all from VERACRUZ, Republic of México,
and distributed as follows: type locality, 4400 ft., 16[1] (including
the type), 6[2], 1[3]; _Cerro Gordo_, 1500 ft., 19; _Teocelo_
[= _Texolo_], 4500 ft., 1; _2 mi. NW Plan del Río_, 1000 ft., 14[4];
_Plan del Río_, 1000 ft., 2[5]; _Carrizal_, 4[2]; Chichicaxtle, 3[2];
_Puente Nacional_, 500 ft., 1[5], 2; _Santa Maria, near Mirador_, 1800 ft.,
10[2]; Boca del Río, 10 ft., 1[5], 8; _Córdoba_ [= _Córdova_], 14[1];
_4 km. WNW Fortín_, 4; _Río Atoyac, 8 km. NW Potrero_, 1; _2 km. N.
Paraje Nuevo_, 1700 ft., 9; _El Xuchil_, _1 mi. W. Paraje Nuevo_, 6[6];
Potrero Viejo, 1700 ft. 15; _Cautlapán_ [= _Ixtaczequitlán_], 4000 ft.,
16; _Micayucan_, 1; 3 km. SE Orizaba, 5500 ft., 3; Río Blanco, 20 km.
WNW Piedras Negras, 400 ft, 7; _29 km. SE Córdoba, Presidio_, 15[4];
_3 km. N Presidio_, 1500 ft., 2; Presidio, 600 meters, 6[3].

_Marginal records._--VERACRUZ: type locality; Chichicaxtle; Boca del
Río, 10 ft.; Río Blanco, 20 km. WNW Piedras Negras, 400 ft; Presidio; 3
km. SE Orizaba, 5500 ft.

[1] American Museum of Natural History.

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

[3] Chicago Natural History Museum.

[4] Univ. Michigan, Museum of Zoology.

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

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


=Baiomys musculus grisescens= Goldman

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

_Type._--Adult female, skin and skull; No. 257083 U. S. Nat. Mus. (Biol.
Surv. Coll.); Comayabuela [= Comayaguela] just south of Tegucigalpa,
3100 feet, Honduras; obtained on March 6, 1932, by C. F. Underwood,
original number 838.

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

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

_Comparisons._--For comparisons with _B. m. pullus_ and _B. m.
handleyi_, see accounts of those subspecies. From _B. m. nigrescens_,
_B. m. grisescens_ differs in: dorsum less blackish (dark brown to
buffy); face buffy below eye rather than brownish-black; venter buffy to
whitish in midline, not sooty gray; forefeet and hind feet flesh-colored
with gray overtones, not dusky to sooty; zygoma bowed, sides less
parallel; braincase and bony palate slightly broader.

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

Felten (1958:136) referred all _B. musculus_ from El Salvador to _B. m.
grisescens_. Although I have not examined the specimens reported on by
Felten (_loc. cit._), I have examined specimens from Lake Atescatempa,
Guatemala (which I refer to _grisescens_), not too distant from Cerro
Blanco, and Finca Las Canarias, Department of Ahuachapan, and Laguna de
Guija, Department of Santa Ana (localities listed by Felten). It would
seem that specimens from these localities might indeed be _grisescens_.
However, specimens that I examined from 1 mi. S Los Planes, and 1 mi. NW
San Salvador were considerably darker than paratypes of _grisescens_ and
were nearly intermediate in color between _nigrescens_ and _pullus_. I
refer the specimens from 1 mi. NW San Salvador, and 1 mi. S Los Planes
to _nigrescens_ rather than to _grisescens_.

There is no positive evidence that _B. m. grisescens_ intergrades with
_B. m. pullus_ to the south in Nicaragua. But, there is a suggestion
that intergradation occurs between these subspecies in a series of 76
skins from La Piedra de Jesús Sabana Grande, Honduras, referable to
_grisescens_. A total of 16 of 76 skins from this locality (21 per cent)
possess the mid-ventral white stripe found in 18 of 20 skins (90 per
cent), from the type locality of _pullus_ in Nicaragua. Further
collection in areas between central Honduras and western Nicaragua may
yield specimens of _B. musculus_ that are intermediate in characters
between _grisescens_ and _pullus_.

_Specimens examined._--Total 149, distributed as follows: GUATEMALA: 1
mi. S Rabinal, 3450 ft., 14; 1/2 mi. N, 1 mi. E Salama, 3200 ft., 10;
Lake Atescatempa, 10[7]. HONDURAS: Cementario, Gracias, 1[8]; Monte
Redondo, 1[8]; El Caliche, Cedros, 1[8]; _La Flor Archaga_, 2[8], 1[9];
Hatillo, 1[8]; _type locality_, 7[8], 6[7] (including the type), 3[9];
_El Zapote_, _Sabana Grande_, 4[8]; La Piedra de Jesús Sabana Grande,
76[8]; _Cerro de las Cuches Sabana Grande_, 5.

_Marginal records._--GUATEMALA: 1/2 mi. N, 1 mi. E Salama, 3200 ft.
HONDURAS: El Caliche, Cedros; Hatillo; La Piedra de Jesús Sabana Grande;
Cementario. GUATEMALA: Lake Atescatempa; 1 mi. S Rabinal, 3450 ft.

[7] United States National Museum (Biol. Surv. Collections).

[8] American Museum of Natural History.

[9] Univ. Michigan, Museum of Zoology.


=Baiomys musculus handleyi= Packard

    _Baiomys musculus handleyi_ Packard, Univ. Kansas Publs., Mus. Nat.
       Hist., 9:399, December 19, 1958.

    _Baiomys musculus musculus_, Goodwin, Bull. Amer. Mus. Nat. Hist.,
       68(1):39-40, December 12, 1934 (part); Miller and Kellogg, Bull.
       U. S. Nat. Mus., 205:512, March 3, 1955 (part).

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

_Type._--Adult female, skin and skull; No. 275604 U. S. Nat. Mus. (Biol.
Surv. Coll.); Sacapulas, El Quiche, Guatemala; obtained on April 24,
1947, by Charles O. Handley, Jr., original number 991.

_Range._--Known only from the type locality in the valley of the Río
Negro. Zonal range: Part of the Chimaltenangan Province of Smith
(1949:235).

_Diagnosis._--Size medium to large for the species; dorsum Wood Brown in
some series to Buffy Brown; guard hairs of dorsum black-tipped, color of
underhairs Avellaneous; hairs white to base in region of chin, throat,
and median venter; in lateral region, hairs Neutral Gray at base; dorsal
surfaces of forefeet and hind feet and ankles white; tail white below,
brownish above; nasals truncate anteriorly; frontoparietal suture
forming an obtuse angle with the suture separating the parietals;
alveolar length of upper molar tooth-row and tail long. Average and
extreme external and cranial measurements for nine adults from the type
locality are as follows: Total length, 121.4 (115-128); length of tail
vertebrae, 50.7 (49-54); length of body, 70.8 (66-77); length of hind
foot, 15.3 (15-16); occipitonasal length, 19.6 (18.8-20.7); zygomatic
breadth, 10.5 (10.2-11.0); postpalatal length, 6.9 (6.4-7.4); least
interorbital breadth, 4.0 (3.9-4.0); length of incisive foramina, 4.2
(4.0-4.5); length of rostrum, 7.2 (7.0-7.7); breadth of braincase, 9.8
(9.7-10.2); depth of cranium, 7.1 (6.8-7.2); alveolar length of
maxillary tooth-row, 3.5 (3.4-3.6); for photographs of skull, see Plate
1_c_, and Plate 3_c_.

_Comparisons._--From _B. m. nigrescens_, _B. m. handleyi_ differs as
follows: everywhere paler; forefeet and hind feet whitish instead of
dusky to sooty; hairs of anterior part of face white instead of brown;
tail bicolored instead of unicolored; anterior tips of nasals truncate
rather than rounded; frontoparietal suture forming obtuse angle with
suture separating parietals instead of forming right angle; tail and
upper molar tooth-row longer.

From _B. m. grisescens_, _B. m. handleyi_ differs in: slightly paler
above and below, primarily as a result of lacking buff-colored hairs;
forefeet and hind feet white, not flesh-colored with gray overtones;
tail bicolored, not unicolored; anterior tips of nasals truncate rather
than flaring; tail and upper molar tooth-row longer.

_Remarks._--_B. m. handleyi_ seems to be restricted to the valley of the
Río Negro, in the region of Sacapulas, Guatemala. Stuart (1954:7) points
out that the Río Negro drops down into a gorge at a place near Sacapulas
and flows northward through a deep canyon for approximately 60
kilometers. The Río Negro, then, flows onto the lowlands of the Yucatán
Peninsula. The habitat is xerophytic in the valley of the Río Negro near
Sacapulas. Stuart (_op. cit._:10) suggests that this xerophytic habitat
may be continuous to a place to the north of Chixoy, Chiapas, where the
vegetation then becomes more mesic. The mesic conditions to the north in
Tabasco and Yucatán probably have restricted the movement of pygmy mice
to the north. No specimens of this mouse are known from the Yucatán
Peninsula or from the State of Tabasco, México. _B. m. handleyi_
intergrades with _B. m. grisescens_ to the south. Specimens from 1 mi. S
Rabinal, and those from a second locality 1/2 mi. N and 1 mi. E Salama,
Guatemala, are intermediate in color of pelage between _handleyi_ and
_grisescens_. Stuart (_op. cit._:5) mentions the continuity of habitat
and tributaries from the Salama Basin into the valley of the Río Negro.
Absence of physiographic and biotic barriers in the corridor between
these two basins probably allows for some gene flow between _handleyi_
and _grisescens_, and results in populations intermediate in color. To
the north and northwest of Sacapulas, the Sierra de los Cuchumatanes
rises abruptly and separates the known geographic range of _handleyi_
from that of _nigrescens_ to the north, while to the west the
cactus-mesquite habitat of _handleyi_ gives way to the oak-pine timber
that, so far as known, does not support _Baiomys_. The difference in
elevation and flora seems to restrict gene flow between _handleyi_ and
the more northern _nigrescens_. The only evidence of integration between
these two subspecies is provided by one specimen from Chanquejelve,
Guatemala. That specimen is intermediate in color between the pale
_handleyi_ and blackish-brown _nigrescens_.

The subspecies closest, geographically, to _B. m. handleyi_ is _B. m.
nigrescens_, from which _B. m. handleyi_ differs more in color than from
any of the other named subspecies, except _B. m. pullus_. There is a
close correlation of pallor of mice and the xeric Río Negro Valley, and
the darkness (melanistic color) of mice and the mesic mountains and
valleys to the north.

_Specimens examined._--Total 49, from GUATEMALA: type locality,
including the type: 12 (U. S. Nat. Mus., Biol. Surv. Coll.), 37 (Amer.
Mus. Nat. Hist.).


=Baiomys musculus infernatis= Hooper

    _Baiomys musculus infernatis_ Hooper, Jour. Mamm., 33:96, February
       18, 1952; Miller and Kellogg, Bull. U. S. Nat. Mus., 205:512,
       March 3, 1955; Hall and Kelson, The Mammals of North America,
       2:661, March 31, 1959.

    _Baiomys musculus musculus_, Hooper, Jour. Mamm., 28:50, February
       15, 1947 (part).

_Type._--Adult male, skin and skull; No. 91497 Univ. of Michigan, Museum
of Zoology; Teotitlán, Oaxaca, Republic of México, obtained on February
24, 1947, by Helmuth O. Wagner, original number 2702.

_Range._--Southeastern Puebla, in the basin drained by the Río Salado
and Río Quiotepec, into northern Oaxaca. Zonal range: Arid Tropical in a
part of the Orizaba-Zempoaltepec Faunal District of the Transverse
Volcanic Biotic Province of Moore (1945:218). Occurs from 3100 feet in
Oaxaca up to 6000 feet in Puebla.

_Diagnosis._--Size medium for the species; dorsum Drab, terminal parts
of individual guard hairs black, Neutral Gray basally, distal parts of
underfur Pinkish Buff, proximally Neutral Gray; sides same color as
dorsum; hairs in region of throat and chin white to base; venter whitish
to Neutral Gray with tinges of Pinkish Buff; dorsal parts of forefeet
and hind feet whitish with flesh-colored undertones, ventral parts
whitish to dusky-gray; tail bicolored, grayish-brown above, white below;
tip of tail not bicolored, instead grayish-brown throughout; ears pale
brown, sparsely haired; incisive foramina long, not constricted
posteriorly. Average and extreme external measurements for 9 adults from
the type locality are as follows: total length, 113.9 (106-122); length
of tail vertebrae, 44.1 (41-48); length of body, 71.0 (65-79); length of
hind foot, 14.8 (13-16); length of ear, 11.9 (11-12). Average and
extreme cranial measurements of 7 adults from the type locality are as
follows: Occipitonasal length, 20.1 (19.7-20.4); zygomatic breadth, 10.4
(10.2-10.6); postpalatal length, 7.3 (7.0-7.7); least interorbital
breadth, 4.2 (4.0-4.4); length of incisive foramina, 4.8 (4.4-5.6);
length of rostrum, 7.2 (6.6-7.5); breadth of braincase, 9.6 (9.5-9.8);
depth of cranium, 7.4 (7.1-7.6); alveolar length of maxillary tooth-row,
3.3 (3.1-3.4); for photographs of skull, see Plate 1_d_, and Plate 3_d_.

_Comparisons._--For comparisons with _B. m. nigrescens_ and _B. m.
brunneus_, see accounts of those subspecies. From _B. m. pallidus_, _B.
m. infernatis_ differs in: sides, ears, and dorsum paler (less of dark
brown); venter whitish gray rather than gray with tinge of buff and
brown; forefeet and hind feet paler; tail bicolored, not unicolored;
incisive foramina longer and not constricted posteriorly; mastoid
process turning dorsally and sickle-shaped at posteriormost point rather
than capitate.

_Remarks._--_B. m. infernatis_ resembles _B. m. handleyi_ more than any
other subspecies in color of pelage and in external and cranial
dimensions. The resemblance in color between _B. m. pallidus_, in
certain parts of its range, and _B. m. handleyi_ may have resulted from
nearly parallel selective forces that gave rise to two subspecies,
widely separated geographically. The same relation obtains between _B.
m. infernatis_ and _B. m. handleyi_. Both inhabit arid river basins. In
them, pale soil and low relative humidity are important passive factors
of selection that give adaptive value to the pale colors of pelage of
both _infernatis_ and _handleyi_.

Specimens from 6-1/2 mi. SW Izucár de Matemores, and 1 mi. SSW Tilapa,
Puebla, are intergrades between _B. m. infernatis_ and _B. m.
pallidus_. These specimens are intermediate in color and cranial
characters between the aforementioned subspecies but possess more of the
pale brown overtones seen in paratypes of _pallidus_, and are best
referred to that subspecies.

_Specimens examined_ (All in Univ. Michigan, Mus. Zool.).--Total 18, all
from the Republic of México and distributed as follows: PUEBLA,
Tepanaco, 6000 ft., 3, Tehuacán, 5400 ft., 3. OAXACA: Type locality,
3100 ft., 12 (including the type).

_Marginal records._--See specimens examined.


=Baiomys musculus musculus= (Merriam)

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

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

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

    [_Peromyscus_] _musculus_, Trouessart, Cat. Mamm., 1:518, 1898.

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

    _Baiomys musculus musculus_, Miller, Bull. U. S. Nat. Mus., 79:137,
       December 31, 1912 (part); Miller, Bull. U. S. Nat. Mus., 128:318,
       April 29, 1924 (part); Ellerman, The Families and Genera of Living
       Rodents, 2:402, March 21, 1941; Poole and Schantz, Bull. U. S. Nat.
       Mus., 178:258, March 6, 1942; Davis, Jour. Mamm., 25:394, December
       12, 1944 (part); Hooper, Jour. Mamm., 28:50, February 15, 1947
       (part); Hall and Villa-R., Univ. Kansas Publs., Mus. Nat. Hist.,
       1:460, December 27, 1949 (part); Hall and Villa-R., Anal. del Inst.
       Biol., 21:196, September 28, 1950 (part); Goldman, Smith. Miscl.
       Coll., 115:336, July 31, 1951 (part); Miller and Kellogg, Bull.
       U. S. Nat. Mus., 205:512, March 3, 1955 (part); Hooper, Occas.
       Papers Mus. Zool. Univ. Michigan, 565:13, March 31, 1955; Hall and
       Kelson, The Mammals of North America, 2:661, March 31, 1959 (part).

    _B._ [_aiomys_] _m._ [_usculus_] _musculus_, Hooper, Jour. Mamm.,
       33:97, February 18, 1952 (part); Packard, Univ. Kansas Publs.,
       Mus. Nat. Hist., 9:400; December 19, 1958.

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

_Type._--Adult female, skin and skull; No. 33437/45460 U. S. Nat. Mus.
(Biol. Surv. Coll.); Colima (City), Colima, Republic of México, obtained
on March 9, 1892, by E. W. Nelson, original number 2055.

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

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

_Comparisons._--For comparisons with _B. m. brunneus_, _B. m.
infernatis_, and _B. m. pallidus_, see accounts of those subspecies.
From _B. m. nigrescens_, _B. m. musculus_ differs in: dorsum paler
throughout (less of blackish brown); region of face and ears paler, more
buff and fawn-colored hairs rather than blackish-brown to grayish hairs;
vibrissae paler; venter paler, less dark gray and less of sooty-colored
undertones, tips of hairs whitish to pale Olive-Buff rather than light
gray at tips becoming darker basally; forefeet and hind feet paler,
whitish to pale buff-color with flesh-colored undertones, not
sooty-colored to dark brown; tail paler below; nasals flaring outward,
not tapering toward midline at anteriormost point; zygoma more massive;
larger in external and cranial dimensions.

_Remarks._--Merriam (1892:170) described _Sitomys_ [= _Baiomys_]
_musculus_ on the basis of 23 specimens (from Colima City, Colima;
Armeria, Colima; Plantinar, and Zapotlán, Jalisco). According to the
original description, _B. musculus_ resembled a small house mouse and
was smaller than any known species of _Sitomys_ except _S. taylori_ [=
_Baiomys taylori_]. From _taylori_, _musculus_ differed in being larger
[in size of body], and in having longer ears and tail, and larger hind
feet. When Allen and Chapman (1897:203) described _Peromyscus_ [=
_Baiomys_] _musculus brunneus_ from Jalapa, Veracruz, the specimens
described by Merriam from Colima and Jalisco became representative of
the nominal subspecies _B. m. musculus_. Osgood (1909:258) assigned
specimens from Colima, Guerrero, Jalisco, Michoacán, Morelos, Oaxaca,
Puebla, Sinaloa, Veracruz, and Zacatecas to the subspecies _musculus_.
Subsequently, Russell (1952:21) named the subspecies _pallidus_ from the
arid lowlands of Morelos; Hooper (1952:96) described the subspecies
_infernatis_ from northern Oaxaca and southeastern Puebla; and Goodwin
(1959:1) described a new subspecies _nebulosus_ from the Oaxaca
highlands. Each of the subspecies mentioned immediately above was
described from within the geographic range assigned to _B. m. musculus_
by Osgood (_loc. cit._). Hall and Kelson (1959:661) mapped the range of
_B. m. musculus_ so as to include Colima, parts of Jalisco, Michoacán,
Guerrero, Oaxaca, and Veracruz. Lukens (1955:159), in a study of the
mammals of Guerrero, has shown that the characters attributed to _B. m.
pallidus_ are not significantly different from those of pygmy mice
studied from Guerrero. He (_loc. cit._) concluded that: (1) if the
specimens of pygmy mice from central Guerrero were typical of the
subspecies _musculus_, then _pallidus_ did not deserve subspecific
recognition, or; (2) the name _B. m. musculus_ should be restricted to
the larger pygmy mice inhabiting the lowlands immediately adjacent to
the Pacific Coast and the area to the north. My data (see Figure 12)
show pygmy mice from southwestern Nayarit, northwestern and central
Jalisco, Colima, and parts of Michoacán to be significantly larger in
certain cranial and external measurements than pygmy mice from Guerrero,
Oaxaca, Morelos, and parts of Puebla. This finding essentially
corroborates Hooper's (1952a:96) findings. It seems advisable,
therefore, to restrict the range of _B. musculus musculus_ to the large
mice inhabiting west-central México and the coastal lowlands of Colima
and Michoacán. The name _pallidus_ is applicable to the smaller mice
occupying Morelos, southwestern Puebla, Guerrero, Oaxaca, and
southwestern Chiapas.

_B. m. musculus_ intergrades with _B. m. pallidus_ in eastern Michoacán
and central and western Guerrero. Specimens from San José Prura and 12
mi. S Tzitzio, Michoacán, though referable to _B. m. musculus_ because
of slightly larger size of crania are intermediate in size and color
between the smaller and slightly darker _pallidus_ to the south and east
and the larger, slightly paler _musculus_ to the northwest.

_Specimens examined._--Total 156 all from the Republic of México, and
distributed as follows: NAYARIT: 3 mi. NNW Las Varas, 150 ft., 1.
JALISCO: 7 mi. W Ameca, 4000 ft., 2[10]; _6 mi. W Ameca_, 4300 ft., 3[10];
_10 mi. S Ameca_, 5800 ft., 1[10]; _13 mi. S, 15 mi. W Guadalajara_, 3;
_13 mi. S, 9-1/2 mi. W Guadalajara_, 1; _3 mi. ENE Santa Cruz de las
Flores_, 1; 27 mi. S, 12 mi. W Guadalajara, 1; _4 mi. NE Autlán_, 3000
ft., 5[10]; _Sierra de Autlán_, 5000 ft., 2[10]; _2-1/2 mi. NNE Autlán_,
3000 ft., 8; 2 mi. SSE Autlán, 1; _5 mi. S Purificación_, 2; Chamela
Bay, 1[10]; _2 mi. N La Resolana_, 1500 ft., 6[10]; _1 mi. N San Gabriel_,
4000 ft., 32[10]; 2 mi. N Cuidad Guzmán, 5000 ft., 1; 3 mi. E Navidad,
4300 ft., 10[10]. COLIMA: _type locality_, 10[11] (including the type); _3
mi. SE Colima_ (_City_), 5[10]; _4 mi. SW Colima City_, 1; Armeria, 200
ft., 8[11]; _Paso del Río_, 20[10].

MICHOACÁN: 12 mi. S Tzitzio, 6[10]; San José Prura, 4[12]; 1 mi. E, 6 mi.
S Tacámbaro, 4000 ft., 3[13]; La Salada, 3[11]; 1/2 mi. SE Coalcomán,
15[10].

_Marginal records._--NAYARIT: 3 mi. NNW Las Varas, 150 ft. JALISCO: 3
mi. E Navidad, 4300 ft.; 27 mi. S, 12 mi. W Guadalajara. MICHOACÁN: 12
mi. S Tzitzio; San José Prura; 1/2 mi. SE Coalcomán. COLIMA: Armeria,
200 ft. JALISCO: Chamela Bay.

[10] Univ. Michigan, Museum of Zoology.

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

[12] Chicago Natural History Museum.

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


=Baiomys musculus nigrescens= (Osgood)

    _Peromyscus musculus nigrescens_ Osgood, Proc. Biol. Soc.
       Washington, 17:76, March 21, 1904; Elliot, Field Columb. Mus. Publ.,
       105(4):136, July 1, 1905; Lyon and Osgood, Bull. U. S. Nat. Mus.,
       62:135, January 15, 1909; Osgood, N. Amer. Fauna, 28:259, April 17,
       1909.

    _Baiomys musculus nigrescens_, Miller, Bull. U. S. Nat. Mus.,
       79:137, March 31, 1912; Miller, Bull. U. S. Nat. Mus., 128:318,
       April 29, 1924; Goodwin, Bull. Amer. Mus. Nat. Hist., 68(1):40,
       December 12, 1934; Ellerman, The Families and Genera of Living
       Rodents, 2:402, March 21, 1941; Poole and Schantz, Bull. U. S. Nat.
       Mus., 178:259, March 6, 1942; Hooper, Jour. Mamm., 28:50, February
       15, 1947; Goldman, Smith. Miscl. Coll., 115:357, July 31, 1951;
       Miller and Kellogg, Bull. U. S. Nat. Mus., 205:513, March 3, 1955;
       Booth, Walla Walla Publs., Dept. Biol. Sci., 20:15, July 10, 1957;
       Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959
       (part).

    [_Peromyscus musculus_] _nigrescens_, Elliot, Field Columb. Mus.
       Publ., 95(4):176, 1904.

    _B._ [_aiomys_] _m._ [_usculus_] _nigrescens_, Goodwin, Bull. Amer.
       Mus. Nat. Hist., 79(2):160, May 29, 1942; Hooper, Jour. Mamm.,
       33:97, February 18, 1952 (part); Packard, Univ. Kansas Publs.,
       Mus. Nat. Hist., 9:399, December 19, 1958.

    _B._ [_aiomys_] _m._ [_usculus_] _musculus_, Booth, Walla Walla
       Publs., Dept. Biol. Sci., 20:15, July 10, 1957 (part).

_Type._--Adult female, skin and skull; No. 76827 U. S. Nat. Mus. (Biol.
Surv. Coll.); Valley of Comitán, Chiapas, Republic of México, obtained
on December 9, 1895, by E. W. Nelson and E. A. Goldman, original number
8719.

_Range._--Southern coastal region and eastern parts of Chiapas,
southeastward into central and southern Guatemala, thence south into El
Salvador (see Figure 10). Zonal range: parts of Lower Austral; also
occurs in parts of the arid division of the Upper Tropical Life-zone,
and in parts of the arid division of the Lower Tropical Life-zone;
approximates a part of the Chiapas Highlands Biotic Province of Goldman
and Moore (1945:349), and parts of the Guatemalan Subregion of Smith
(1949:235).

_Diagnosis._--Size medium to small for the species; dorsum Vandyke Brown
mixed with blackish, individual hairs black-tipped with a subterminal
band of Warm Buff, Neutral Gray at base; guard hairs of dorsum black
distally, Neutral Gray basally; hairs on sides grayish-brown, facial
region like dorsum; chin buffy-brown; vibrissae brown, ventrally some
white; venter creamy-buff to grayish, individual hairs creamy-buff at
tips, gray basally; in region of throat and chin, hairs tipped with
Ochraceous-Buff; dorsal surface of forefeet and hind feet dull whitish
gray to brownish-black; tail indistinctly bicolored, dusky above,
grayish to brownish below; incisive foramina short, wide medially;
average and extreme external and cranial measurements of 15 adults from
6 mi. NW Tonalá, Chiapas, are as follows: total length, 107.5 (100-116);
length of tail vertebrae, 41.1 (33-48); length of body, 66.1 (62-73);
length of hind foot, 15.0 (14-16); length of ear, 10.9 (10-12);
occipitonasal length, 18.9 (18.4-19.7); zygomatic breadth, 9.8
(9.4-10.2); postpalatal length, 6.9 (6.6-7.4); least interorbital
breadth, 3.7 (3.5-3.8); length of incisive foramina, 4.4 (4.1-4.8);
length of rostrum, 6.7 (6.1-7.1); breadth of braincase, 9.2 (9.0-9.4);
depth of cranium, 6.9 (6.5-7.3); alveolar length of maxillary tooth-row,
3.1 (2.9-3.2); for photographs of skull, see Plate 1_f_, and Plate 3_f_.

_Comparisons._--For comparisons with _B. m. handleyi_, _B. m.
grisescens_, _B. m. musculus_, _B. m. pallidus_, and _B. m. pullus_, see
accounts of those subspecies.

From _B. m. brunneus_, _B. m. nigrescens_ differs in: dorsum
blackish-brown rather than reddish to ochraceous brown; face and ears
brownish-black rather than brownish with tinges of ochraceous; vibrissae
darker; forefeet and hind feet darker; venter with more grayish tones;
dorsalmost part of zygomatic plate projects farther anteriorly;
interparietal oval to diamond-shaped and narrower anteroposteriorly;
zygomata narrower at anteriormost part; slightly smaller in most cranial
and external measurements.

From _B. m. infernatis_, _B. m. nigrescens_ differs in: dorsum darker;
region of face and ears darker; venter buffy to gray rather than
whitish-buff; vibrissae darker; forefeet and hind feet darker; tail
darker above and below; incisive foramina shorter, more constricted
laterally; cranium slightly smaller in most dimensions.

_Remarks._--Hooper (1952a:93-94) reported specimens from the coastal
strip of southern Chiapas as the most intensely pigmented, whereas,
specimens from central and western Chiapas were distinctly paler. Crania
of specimens from the coastal region of southern Chiapas were smaller
than crania from the central highlands and mountains of Chiapas. My
studies essentially corroborate the findings of Hooper. The gradation of
color between the pale brown _pallidus_ to the north in Oaxaca, and the
brownish-black _nigrescens_ to the south in Chiapas is extremely
gradual. Specimens from the central and western parts of Chiapas (see
Figure 10 for localities) are difficult to assign to either _pallidus_
or _nigrescens_. Equal justification exists for assignment to either
subspecies. I have assigned the specimens to _nigrescens_ because they
are geographically closer to the type locality of _nigrescens_.
Specimens from Reforma, Oaxaca (assigned by Hooper, 1952a:93-94, to
_nigrescens_), are nearly identical in size and color to paratypes of
_pallidus_. I assign the Reforma specimens to _pallidus_.

The darkest of all the specimens examined and assigned to _nigrescens_
are from 1 mi. NW San Salvador and 1 mi. S Los Planes, El Salvador. The
variations in color in this subspecies closely correspond to degree of
relative humidity; the palest samples are from areas of low relative
humidity and the darkest are from areas of high relative humidity. In
view of the present state of differentiation of specimens from the
southern coastal areas of Chiapas and mountainous areas of El Salvador,
it would seem that populations there might be incipient subspecies.

_Specimens examined._--Total 319. CHIAPAS: _17 mi. W Bochil_, 1[14]; _15
mi. W Bochil_, 1[14]; _14 mi. W Bochil_, 1[14]; Bochil, 6[15]; Ocuilapa,
3500 ft., 5[16]; _5 mi. NNW Tuxtla Gutiérrez_, 9; _11 km. W Tuxtla
Gutiérrez_, 800 m., 2[15]; _10 km. W Tuxtla Gutiérrez_, 800 m., 2[15];
_Tuxtla Gutiérrez_, 2600 ft., 8[16], 11; _Ocozocoautla_, 10[15], 2[16]; 25
mi. E Comitán, Las Margaritas, 1250 m., 5[17], 24[15]; Cintalpa, 555 m.,
1[14], 18[15], 3[17]; _Jiquilpilas_, 2000 ft., 1[16]; San Bartolome, 3[16];
_type locality_, 5700 ft., 26[16] (including the type); 15 mi. SW Las
Cruces, 1; Villa Flores, 600 m., 12[15]; _23 mi. S Comitán_, 1[14]; _15
mi. S, 2 mi. E La Trinitaria_, 4; _30 mi. S Comitán_, 2[14]; 35 mi. S
Comitán, 1[14]; _3 mi. E Arriga_, 1[14]; 6 mi. NW Tonalá, 19; _Tonalá_,
8[16]; _Los Amates_, 1[14]; Pijijiapan, 10 m., 7[15]; Mapastepec, 45 m.,
25[15], 4[17].

GUATEMALA: Chanquejelve, 1[14]; _Nentón_, 3000 ft., 1[16]; Jacaltenango,
5400 ft., 8[16]; La Primavera, 5[14]; 4 mi. S Guatemala City, 4700 ft., 3;
_5 mi. S Guatemala City_, 4050 ft., 10; _6 mi. S Guatemala City_, 4680
ft., 1; _Lake Amatitlán_, 4500 ft., 13[16]; El Progresso (Distrito Santa
Rosa), 3[15]; _2 mi. N, 1 mi. W Cuilapa_, 2980 ft., 1[14]; _1 mi. WSW El
Molino_ (_Distrito Santa Rosa_), 2; _2-1/2 mi. W, 2-1/4 mi. N San
Cristobal_, 2900 ft., 1; El Zapote, 1[15].

EL SALVADOR: 1 mi. NW San Salvador, 29; 1 mi. S Los Planes, 15.

_Marginal Records._--CHIAPAS: Bochil; 25 mi. E Comitán, Las Margaritas,
1250 ft. GUATEMALA: Chanquejelve; La Primavera; Jacaltenango, 5400 ft.;
4 mi. S Guatemala City, 4700 ft.; El Progresso. _El Salvador_: 1 mi. NW
San Salvador; 1 mi. S Los Planes. GUATEMALA: El Zapote. CHIAPAS:
Mapastepec, 45 m.; Pijijiapan, 10 m.; 6 mi. NW Tonalá; 15 mi. SW Las
Cruces; Cintalpa, 555 m.; Ocuilapa, 3500 ft.

[14] American Museum of Natural History.

[15] Univ. Michigan, Museum of Zoology.

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

[17] University of Florida Collections.


=Baiomys musculus pallidus= Russell

    _Baiomys musculus pallidus_ Russell, Proc. Biol. Soc. Washington,
       January 29, 1952; Davis and Russell, Jour. Mamm., 35:75, February
       10, 1954; Miller and Kellogg, Bull. U. S. Nat. Mus., 205:512; Hall
       and Kelson, The Mammals of North America, 2:662, March 31, 1959.

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

    _Peromyscus musculus_ [_musculus_], Osgood, N. Amer. Fauna, 28:257,
       April 17, 1909 (part).

    _Baiomys musculus musculus_, Miller, Bull. U. S. Nat. Mus., 79:137,
       December 31, 1912 (part); Miller, Bull. U. S. Nat. Mus., 128:318,
       April 29, 1924 (part); Davis, Jour. Mamm., 25:394, December 12, 1944
       (part); Hooper, Jour. Mamm., 28:50, February 15, 1947 (part);
       Goldman, Smith, Miscl. Coll., 115:336, July 31, 1951 (part); Miller
       and Kellogg, Bull. U. S. Nat. Mus., 205:512, March 3, 1955 (part);
       Booth, Walla Walla Publs., Dept. Biol. Sci., 20:15, July 10, 1957
       (part); Hall and Kelson, The Mammals of North America, 2:661,
       March 31, 1959 (part); Goodwin, Amer. Mus. Novitates, 1929:1,
       March 5, 1959.

    _B._ [_aiomys_] _m._ [_usculus_] _musculus_, Hooper, Jour. Mamm.,
       33:97, February 18, 1952 (part).

    _B._ [_aiomys_] _m._ [_usculus_] _nigrescens_, Hooper, Jour. Mamm.,
       33:97, February 18, 1952 (part).

    _Baiomys musculus nebulosus Goodwin_, Amer. Mus. Novitates, 1929,
       March 5, 1959.

_Type._--Adult female, skin and skull; No. 4501 Texas A&M Cooperative
Wildlife Collection; 12 kms. NW Axochiapán, 3500 feet, Morelos, Republic
of México, obtained on July 28, 1950, by W. B. Davis, original number
5112.

_Range._--Guerrero thence eastward into Morelos and west central Puebla
along the southern edge of the Transverse Volcanic Biotic Province
(Goldman and Moore, 1945:349), south into Oaxaca, see Figure 10. Zonal
range: largely Arid Lower Tropical Subzone of Goldman (1951:330). Occurs
from near sea level in Oaxaca and Guerrero up to 6550 feet in Oaxaca.

_Diagnosis._--Size medium for the species; dorsum Buffy Brown in palest
series to Olive-Brown in darkest series, individual hairs Warm Buff,
Neutral Gray basally, some with black tips and a subterminal band of
Warm Buff, guard hairs of dorsum black-tipped, gray basally; hairs on
sides creamy-buff, gray basally; face same color as back fading to white
on throat; vibrissae white-tipped, pale brown basally; venter, whitish
with tinges of buff on lower throat, individual hairs having tips white
to buffy-white, light gray basally; dorsal surface of forefeet and hind
feet whitish to flesh-color; tail indistinctly bicolored, brownish
above, grayish brown below; zygoma bowed as in _B. m. grisescens_; tail
short; average and extreme external and cranial measurements for 17
adults from Tehuantepec, Oaxaca, are: total length, 117.3 (110-126);
length of tail vertebrae, 46.9 (41-51); length of body, 70.4 (65-76);
length of hind foot, 15.8 (15-16); occipitonasal length, 18.9
(18.2-20.1); zygomatic breadth, 10.1 (9.7-10.6); postpalatal length, 6.9
(6.6-7.5); least interorbital breadth, 3.8 (3.6-3.9); length of incisive
foramina, 4.4 (4.2-4.7); length of rostrum, 6.7 (6.3-7.2); breadth of
braincase, 9.3 (8.7-9.7); depth of cranium, 6.6 (6.4-6.8); alveolar
length of maxillary tooth-row, 3.2 (3.1-3.4); for photographs of skull,
see Plate 1g, and Plate 3g.

_Comparisons._--For comparisons with _B. m. brunneus_ and _B. m.
infernatis_, see accounts of those subspecies.

From _B. m. musculus_, _B. m. pallidus_ differs in: dorsum more
olive-gray and brown, less ochraceous on either side of mid-dorsal
region; face below eye grayish, not buffy; sides gray with buffy
overtone, not creamy with light yellow overtones; venter grayish-white
rather than an olive-buff; zygomata more tapering anteriorly; maxillary
part of zygoma narrower when viewed from above; external and cranial
dimensions smaller.

From _B. m. nigrescens_, _B. m. pallidus_ differs in: dorsum paler,
fewer black hairs medially; face paler, less sooty; vibrissae brownish
with white tips rather than black with brownish tips; venter paler;
dorsal surface of forefeet and hind feet whitish to flesh-colored rather
than sooty to dusky-white; tail paler; nasals slightly more attenuated;
averaging slightly larger in external and cranial measurements.

_Remarks._--Russell (1952:21) described _pallidus_, on the basis of
specimens from the arid Balsas Basin, of Morelos, as pale gray dorsally.
After examining the original material from Morelos, I find the dorsal
color of _pallidus_ to be much closer to a buffy brown than a pale
grayish. Even so, smaller size differentiates _pallidus_ from
_musculus_. _B. m. infernatis_, not _B. m. pallidus_, is the most pallid
of all named subspecies of _B. musculus_.

_B. m. pallidus_ intergrades to the northwest with _B. m. musculus_, to
the northeast with _B. m. infernatis_, and to the southeast with _B. m.
nigrescens_.

According to Goodwin (1959:2), _B. m. nebulosus_ (named on the basis of
one specimen) differs from _B. m. musculus_ [= _pallidus_] from southern
Oaxaca in: darker and longer pelage; larger skull; interorbital region
broader and less constricted posteriorly. From _B. m. nigrescens_ and
_B. m. brunneus_, _B. m. nebulosus_ differs as follows: pelage longer
and softer; skull larger.

Study of specimens of _B. musculus_ from Oaxaca reveals considerable
variation in external and cranial measurements as well as color,
corresponding to that reported by Goodwin (_loc. cit._). Specimens from
higher altitudes average somewhat darker and larger in external and
cranial size than those at lower elevations. These differences seem to
be microgeographic and not of subspecific rank. Among specimens that I
have studied in Oaxaca are several from different localities (KU 63052,
an adult male, from 3 mi. W Miahuatlán; KU 68964, an adult male from 3
mi. W Mitla, 6000 ft.; KU 63055, an adult female from 3 mi. S
Candelario, 1200 ft.) that, according to Goodwin (_in. litt._) match
_nebulosus_ in reported color, size of body and skull (except for the
region of the rostrum).

Two of the three specimens (KU 63052 and 63055) are the darkest of a
series in which the palest are inseparable from _B. m. pallidus_.
Goodwin, who kindly compared the three specimens with the type of
_nebulosus_, mentioned (_in. litt._) that the skull of the type has a
slenderer rostrum. Included in the series of skulls of _B. m. pallidus_
from 3 mi. W Mitla are several adults (not seen by Goodwin) with slender
rostra. _B. m. nebulosus_ is judged to be a synonym of _B. m. pallidus_.

Populations of pygmy mice occurring in partially isolated areas of
highland in Oaxaca seem to me to be incipient subspecies.

_Specimens examined._--Total 824 all from the Republic of México and
distributed as follows: PUEBLA: 2 mi. S Atlixco, 5800 ft., 1; _1 mi. SSW
Tilapa_, 5800 ft., 2; _6 mi. SW Izucár de Matemores_, 7; _Piaxtla_, 3900
ft., 4[18]; Acatlán, 4100 ft., 1. MORELOS: 5 mi. W Tepoztlán, 6000 ft.,
7[19]; _1 mi. W Tepoztlán_, 6000 ft., 9[19]; _2 mi. SW Tepoztlán_, 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; _Teloloapán_,
20[19], 5[24]; _1 km. N Chapa_, 1470 m., 6; _Chapa_, 1470 m., 5; El Limón,
3[18]; 2-1/2 mi. W Mexcala, 2100 ft., 1[20]; _Río 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
Rincón_, 2600 ft., 2[20]; _8 mi. SW Tierra Colorado_, 600 ft., 1[20]; Río
Aguacatillo, _30 km. N Acapulco_, 1000 ft., 3[20]; 5 mi. ESE Tecpán, 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
Huajuapám_, 5000 ft., 1; 2 mi. NW Tamazulapán, 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 Matalán_, 5950 ft., 14; _Lachiguiri_, 2[23]; _Tres
Cruces_, 10[23]; _Agua Blanca_, 11[23]; _San José_, 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];
_Juchitán_, _Laguna Superior_; Manteca, 8[23], 1[23]; San Bartolo, 3000
ft., 1[18]; _Ejutla_, 1400 m., 21[19]; _El Bambita_, _Tequisitlán_ 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]; _Rincón Bamba_, 11[23];
_3 mi. W Miahuatlán_, 5300 ft., 1; _Miahuatlán_, 12[19], 1[23], 6[24]; _San
Juan Acaltepec_, 5[23]; _Zapotitlán_, 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 Tepoztlán, 6000 ft. PUEBLA: 2 mi.
S Atlixco, 5800 ft.; Acatlán, 4100 ft. OAXACA: 2 mi. NW Tamazulapán,
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 Limón; 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, Estelí, 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 Río Estelí, 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 Estelí_, 8;
_8 mi. NNW Estelí_, 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, Querétaro, 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 Potosí, Tamaulipas, eastern Coahuila,
Nuevo León, into south, southeast, and north-central Texas. Southern
margin of range in central México 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 México (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, Querétaro, 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 Michoacán. 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 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, 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 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, 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 Río Grande de
Santiago and northwest of Guadalajara (4 mi. SE Ahuacatlán; 1 mi. E
Ixtlán; Etzatlán) 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 Michoacán, 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 Río
Tepalcatepec (10 mi. S, 1 mi. W Apatzingán) in Michoacán resemble
paratypes of _allex_. Intergradation probably occurs to the north with
_analogous_.

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 to _allex_. The median part of the belly of the eight specimens
is buff-colored rather than whitish-gray as in typical _allex_; the
mid-dorsal region also averages darker than in any other specimens
referred to _allex_. 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 to _allex_. Possibly the
population represented by the eight specimens is an incipient
subspecies.

There is no evidence of hybridization or intergradation of populations
of _B. t. allex_ with any population of _B. musculus_ where the two
species occur together.

_Specimens examined._--Total 233, all from the Republic of México,
distributed as follows: NAYARIT: 3 mi. SE Mirador, 7; _2 mi. S.
Compostela_, 2900 ft., 5; _4 mi. 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 analogous_ Osgood, 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, see Figure 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;
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, see Plate 2_a_ and Plate 4_b_.

_Comparisons._--For comparisons with _B. t. allex_, _B. t. canutus_, _B.
t. paulus_, and _B. t. fuliginatus_, see accounts of those subspecies.
From _B. t. taylori_, _B. t. analogous_ differs 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 of _analogous_ becomes 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_, like _B. t.
subater_ and _B. t. fuliginatus_, is uniformly brownish-black. Both
_analogous_ and _fuliginatus_ occur 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. analogous_ intergrades with _B. t. paulus_ (see account of that
subspecies) and _B. t. allex_ south and west of Lago de Chapala in
Jalisco. Additional specimens are needed from Querétaro and San Luis
Potosí in order to ascertain whether or not _B. t. analogous_
intergrades with _B. t. fuliginatus_ or _B. t. taylori_. Specimens from
western Jalisco, in the past referred to _B. t. analogous_, are
referable to _B. 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 both _B. t. allex_ and _B. t. analogous_. For
example, specimens from 2 mi. N Ciudad Guzmán resemble _analogous_ on
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 typical _analogous_ (being like _allex_ instead).
The dorsal surface of the forefeet are sooty to light brownish (as in
_analogous_), whereas, the hind feet are flesh-colored (as in _allex_).
Another series of specimens from 4 mi. W León, Guanajuato, are
intergrades between _B. t. analogous_ and _B. t. paulus_. These
specimens are grayish to brownish on the dorsum, have sooty forefeet and
hind feet (more nearly as in _analogous_ than in _paulus_), are
grayish-white on the venter, and have a distinctly bicolored tail
(resembling that of _paulus_ more than that of _analogous_). When the
average of cranial characters is considered, both series are best
referred to _analogous_.

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 of _analogous_. 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 typical _analogous_. The hairs of these individuals
average longer than in other populations of _analogous_. Skulls of the
specimens from the pedregal are indistinguishable from those of
paratypes of _analogous_. 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; _2-1/2 mi. E Tepatitlán_, 6200 ft., 15; _2 mi. S, 1/2 mi. W
Tepatitlán_, 9; _near Tepatitlán_, 2; _5 mi. SW Arrandas_, 6700 ft., 6;
_2 mi. E Zapotlanejo_, 23; _2-1/2 mi. E Puente Grande_ (_5-1/2 mi. 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, 9-1/2 mi. 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; _1-1/2 mi. N Mazatmitla_, 6[29];
_1/2 mi. 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; _4-1/2 mi. 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; _1-1/2 mi. 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]; _Pátzucuaro_ 9[31], 4[30], 4[29]; Uruapan, 1[29]; _E
Uruapan_, 12; _2-1/2 mi. 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, 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; _3/4 mi. 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; _3/4
mi. 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 ater_ Blossom 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, see Figure 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 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 9-1/2 mi. W New Mexico State Line, 5-1/2 mi. 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, see Plate 2_b_, and Plate 4_c_.

_Comparisons._--For comparisons with _B. t. canutus_, see account of
that subspecies. From _B. t. paulus_, the subspecies to the southeast,
_B. t. ater_ differs 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) described _B. t. ater_ as the
darkest of the known subspecies. It is dark, but specimens from some
parts of the ranges of _B. t. analogous_, _B. t. fuliginatus_, and _B.
t. subater_ exceed in melanins the darkest individuals of _ater_. Blair
and Blossom (1948:5) also concluded by the use of an Ives tint
photometer that _B. t. subater_ was significantly darker than _B. t.
ater_.

When paratypes of _ater_ and specimens of _B. t. paulus_ are compared,
the darkest individuals of _ater_ exceed but slightly the darkest of
_paulus_. The darkest specimens of _paulus_ occur in southern Zacatecas,
and northern Jalisco, and the palest of the series are in northern
Durango and southern Chihuahua. When paratypes of _ater_ and _paulus_
are compared, the difference in color is readily distinguishable.
Specimens from 1-1/2 mi. N San Francisco, in northern Chihuahua, appear
to be intermediate in color between _ater_ and _paulus_ except for a
faint tinge of buff ventrally. In characters of the crania, these
specimens resemble _ater_ and 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 of _ater_, but the venter has only the
faintest suggestion of the buffy wash. Crania of these specimens from
New Mexico are inseparable from those of paratypes of _ater_, and the
specimens are, therefore, referred to _ater_.

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 of _ater_ compared to variation detected in other
subspecies of _Baiomys 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 of _ater_ may result from
uniform environmental conditions, which have served to select for
uniform characters in the populations. All of the other wide-ranging
subspecies of _B. taylori_ occupy more diverse habitats than _ater_.
Secondly, the rather abrupt change in the cline of measured characters
of the crania between _ater_ and _paulus_ in central Chihuahua suggests
a secondary zone of intergradation. The probable cessation of gene flow
in the past between these two subspecies, allowing _ater_ to be isolated
for a time, may also, in part, account for the relative lack of
variability in the crania of _ater_.

_Specimens examined._--Total 58, distributed as follows: ARIZONA:
_Graham County_: 1-1/2 mi. SW Ft. Grant, Graham Mts., 1[39]; _Pima
County_: 1-1/2 mi. ENE Greaterville, Thurber Ranch, 2[39]; _Santa Cruz
County_: Patagonia, 3[39]; _Cochise County_: _9 mi. W Hereford_, 10[43];
type locality, 2[43] (including the type); _5 mi. W Hereford_, 5[43];
9-1/2 mi. W New Mexico State Line, 5-1/2 mi. N Mexican border, 20[42]; _3
mi. E, 1 mi. N Chiricahua_, 1[42]. NEW MEXICO: _Hidalgo County_: 18 mi.
S, 2 mi. W Animas, 2; _22 mi. S, 2 mi. W Rodeo_, 6000 ft., 1[40]; _22 mi.
S, 2 mi. E Rodeo_, 6000 ft., 3[40]; 25-1/2 mi. S Animas, 6200 ft. (in Big
Bill Canyon), 1[40]. CHIHUAHUA: _5-1/2 mi. N, 2 mi. W San Francisco_,
5100 ft., 1; _2-1/2 mi. N, 3 mi. W San Francisco_, 5200 ft., 1; 1-1/2
mi. N San Francisco, 5100 ft., 4; Casas Grandes, 4300 ft., 1[41].

_Marginal records_--ARIZONA: 1-1/2 mi. SW Ft. Grant, Graham Mts. NEW
MEXICO: 18 mi. S, 2 mi. W Animas; 25-1/2 mi. S Animas (in Big Bill
Canyon). CHIHUAHUA: 1-1/2 mi. N San Francisco; Casas Grandes. ARIZONA:
Patagonia; 1-1/2 mi. ENE Greaterville, Thurber Ranch.

[39] University of Illinois, Museum of Natural History.

[40] University of New Mexico.

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

[42] University of Arizona.

[43] Univ. Michigan, Museum of Zoology.


=Baiomys taylori canutus=, new subspecies

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

    _Peromyscus musculus_ [_musculus_], Osgood, N. Amer. Fauna, 28:256,
       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); Burt, Miscl. Publ., Mus. Zool., Univ.
       Michigan, 39:54, February 14, 1938; Goldman, Smith. Miscl. Coll.,
       115:373, July 31, 1951 (part); Miller and Kellogg, Bull. U. S. Nat.
       Mus., 205:512, March 3, 1955 (part); Hooper, Occas. Papers Mus.
       Zool., Univ. Michigan, 565:13, March 31, 1955; Hall and Kelson, The
       Mammals of North America, 2:659, March 31, 1959 (part).

    _Baiomys musculus musculus_, Goldman, Smith. Miscl. Coll., 115:336,
       July 31, 1951 (part).

_Type._--Adult male, skin and skull; No. 62075, University of Kansas,
Museum of Natural History; 1 mi. S Pericos, Sinaloa, Republic of México;
obtained on June 14, 1954, by A. A. Alcorn, original number 1754.

_Range._--Central Nayarit northward through western Sinaloa, to as far
north as south-central Sonora, see Figure 11. Zonal range: Lower arid
tropical, closely approximating the Sinaloan Biotic Province of Goldman
and Moore (1945:349). Occurs from near sea level at Escuinapa (43 feet),
Sinaloa, to 3200 feet at a place 2 mi. WNW Tepic, Nayarit.

_Diagnosis._--Dorsal ground color Buffy Brown (some specimens near Olive
Brown); proximal fourth of individual guard hairs of dorsum
black-tipped, distal three-fourths dark grayish; dorsal underfur
black-tipped having subterminal band of Buffy Brown; hair around eyes
buffy to base; belly Pallid Neutral Gray with overtones of buff;
individual hairs in region of chin whitish-gray to bases; vibrissae
blackish to bases except ventralmost, those being white to base; tail
Dark Olive above, slightly paler below. Average and extreme external
measurements of 13 adults from 15 mi. N Rosario, Chelé, Sinaloa, 300
ft., are as follows: Total length, 109.6 (99-120); length of tail, 43.4
(38-49); length of body, 66.2 (58-75); length of hind foot, 11.2
(10-12). Average and extreme cranial measurements of 19 adults from the
same place are as follows: occipitonasal length, 18.2 (17.7-18.9);
zygomatic breadth, 9.6 (9.2-10.1); postpalatal length, 6.9 (6.5-7.3);
least interorbital breadth, 3.6 (3.4-3.8); length of incisive foramina,
3.9 (3.5-4.2); length of rostrum, 5.9 (5.5-6.6); breadth of braincase,
8.7 (8.3-8.9); depth of cranium, 6.5 (6.2-6.7); alveolar length of
maxillary tooth-row, 3.1 (3.0-3.2); breadth of zygomatic plate, 1.8
(1.6-2.0); for photographs of skull, see Plate 2_c_, and Plate 4_d_.

_Comparisons._--From _B. t. ater_, _B. t. canutus_ differs in: dorsum
slightly grayer; belly whitish to pale-gray with only faint tones of
buff, rather than cinnamon-buff to buff-gray; forefeet and hind feet
flesh-colored to grayish above instead of whitish to flesh-colored; tail
paler above, less hairy, scales more evident; interparietal relatively
larger from anteriormost to posteriormost points; incisive foramina
tapering less abruptly posteriorly, not constricted towards midline;
over-all size of body and cranium somewhat larger.

From _B. t. paulus_, _B. t. canutus_ differs in: dorsum grayish-brown
rather than fawn-colored (not differing appreciably from extremes of
darker brown specimens of _paulus_); forefeet and hind feet
flesh-colored to grayish above rather than white above; tail less
hairy, unicolored to faintly bicolored rather than distinctly bicolored;
braincase slightly larger; alveolar length of maxillary tooth-row
slightly less.

From _B. t. analogous_, _B. t. canutus_ differs in: dorsum paler, less
of dark brown hues; belly paler; forefeet and hind feet slightly paler,
less sooty above; tail less hairy, paler and having scales evident;
jugal of zygoma extending ventrally to a point immediately above,
instead of below, level of alveolus of upper molars; nasals more nearly
truncate anteriorly; infraorbital foramina less deeply notched toward
midline of skull; body and skull averaging smaller throughout.

From _B. t. allex_, _B. t. canutus_ differs in: dorsal ground color
grayish rather than fawn color having grayish overtones; underfur on
dorsum darker gray; dorsal surface of forefeet and hind feet
flesh-colored to grayish rather than flesh-colored; incisive foramina
tapering to a point posteriorly rather than rounded posteriorly;
interparietal relatively smaller; body and skull averaging larger
throughout.

_Remarks._--Burt (1938:54) reluctantly assigned specimens from Ciudad
Obregón to _B. t. paulus_, probably being influenced by the resemblance
in size. He suggested that, perhaps, a distinct subspecies occurs in the
State of Sonora. Study of larger series of specimens than were available
to Burt reveals that populations of pygmy mice inhabiting the northwest
coastal plains of México are indeed distinct.

The darkest of the material assigned to _canutus_ is from Nayarit (for
specific localities see specimens examined). According to Tamayo
(1949:Carta de Suelos), color of soil changes from chestnut in northern
Sinaloa to black in southern Sinaloa and northern Nayarit. There seems,
therefore, to be a close correlation between color of pelage and color
of soil in this area. In Nayarit, particularly in the central and
southern parts, the mice are intermediate in color between the paler,
grayer population to the north and the more brownish samples,
representative of _allex_ to the south. The coastal vegetation changes
from the arid tropical thorn forests of the north and central parts of
Sinaloa to a savannah in Nayarit, thence to a tropical deciduous forest
farther south (see Leopold, 1950:508).

In size and color, specimens from 3 mi. SE Tepic and 2 mi. SW Rosa
Morada are intermediate between the larger, grayer _canutus_ and the
smaller, light-brownish _allex_. In size of cranium, these specimens are
more nearly like _canutus_, and are referred to that subspecies. Mice
from the western coastal plain are relatively homogeneous as regards
size of body and skull, except that those from 13.5 mi. S Acaponéta,
Nayarit, average somewhat larger.

_B. t. canutus_, like _B. t. subater_, is predominantly a lowland or
coastal subspecies. The pallor of the former, that lives on generally
paler soils, presumably is of adaptive value.

Pygmy mice are seemingly rare in the northern part of the range of this
subspecies. J. Raymond Alcorn and Albert Alcorn were successful in
collecting only two specimens from the type locality after three
successive nights of trapping with 100 traps set each night. Only six
specimens are known from Sonora. These were obtained in the irrigated
regions of Ciudad, Obregón, and Navajoa. Charles Sibley obtained one
specimen 10.6 mi. SE Ciudad Obregón in a "maguey field." I obtained one
specimen 1 mi. NNW Navajoa in a sparse grassway, 20 feet wide, bordering
an open sewer, which coursed northward into the Río Mayo. Irrigated
wheat fields bordered the grassway and ditch.

_Specimens examined._--Total 70 all from the Republic of México and
distributed as follows: SONORA: [Ciudad] Obregón, 4[44]; 10.6 mi. SE
[Ciudad] Obregón, 1[45]; 1 mi. NNW Navajoa, 1. SINALOA: type locality, 2
(including the type); Culiacán, 175 ft., 2[46]; Mazatlán, 1[48]; _15 mi. N
Rosario, Chelé_, 300 ft., 35[47]; Rosario, 3[46]; Escuinapa, 5[48];
_Railroad Station Escuinapa_, 43 ft., 2[45]. NAYARIT: Acaponéta, 4[46];
_13.5 mi. S Acaponéta Junction_, 6[49]; 2 mi. SW Rosa Morada, 2; _2 mi.
WNW Tepic_, 3200 ft., 1; 3 mi. SE Tepic, 1.

_Marginal records._--SONORA [Ciudad] Obregón. SINALOA: type locality;
Escuinapa. NAYARIT: Acaponéta; 3 mi. SE Tepic. SINALOA: Mazatlán.

[44] Coll. Univ. California, Los Angeles.

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

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

[47] Univ. Michigan, Museum of Zoology.

[48] American Museum of Natural History.

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


=Baiomys taylori fuliginatus=, new subspecies

    _Baiomys taylori taylori_, Dalquest, Louisiana State Univ. Studies
       (Biol. Sci. Ser.) 1:155, December 28, 1953 (part).

    _Baiomys taylori taylori_, Booth, Walla Walla Publs. Dept. Biol.
       Sci., 20:15, July 10, 1957 (part).

_Type._--Adult male, skin and skull; No. 36765, University of Kansas,
Museum of Natural History; 10 mi. E, 2 mi. N Ciudad del Maíz, 4000 ft.,
San Luis Potosí, Republic of México; obtained on January 17, 1950, by J.
R. Alcorn, original number 10400.

_Range._--Occurs in the Sierra Madre Oriental of the northeastern third
of San Luis Potosí. Zonal range: Upper Tropical (see Dalquest, 1953:10);
approximates a part of the Sierra Madre Oriental Biotic Province of
Goldman and Moore (1945:349, 356). Occurs from 2000 feet at El Salto up
to 4000 feet at Ciudad del Maíz.

_Diagnosis._--Size large for the species; ground color of dorsum
Chaetura Drab; individual guard hairs of dorsum black to base, distal
fourth of hairs of underfur in posterior half of dorsum tipped with
grayish-brown, proximal three-fourths Dark Neutral Gray; in anterior
region of dorsum, posterior to ears, distal third of hairs grayish-brown
and proximal two-thirds Dark Neutral Gray to base; sides slightly paler
than dorsum; ground color of belly Neutral Gray, individual hairs of
belly and throat tipped with Pallid Neutral Gray, basally Deep Neutral
Gray to Dark Neutral Gray; tips of individual hairs of face
Ochraceous-Tawny; lateral vibrissae whitish, dorsal and ventral
vibrissae black to base; forefeet and hind feet sooty above and below,
thigh bearing some white-tipped hairs; tail near Chaetura Drab above,
Pale Neutral Gray below; anterior part of jugal projecting slightly
ventrally and forming small protuberance at point of articulation with
maxillary part of zygoma; jugal extending anteriorly nearly to lacrimal.
In most cranial measurements averaging as large as _B. t. analogous_.
Average and extreme measurements of the type and three additional
paratypes, all adults, are: total length, 105.5 (101-109); length of
tail, 39.8 (35-42); length of body, 65.8 (63-68); length of hind foot,
14.3 (14-15); length of ear from notch, 11 (11); occipitonasal length,
18.1 (18.1-18.8); zygomatic breadth, 9.6 (9.3-9.8); postpalatal length,
6.5 (6.0-6.7); least interorbital breadth, 3.4 (3.3-3.6); length of
incisive foramina, 4.0 (3.8-4.2); length of rostrum, 6.3 (6.1-6.4);
breadth of braincase, 8.8 (8.6-8.9); depth of cranium, 6.7 (6.5-6.8);
alveolar length of maxillary tooth-row, 3.2 (3.1-3.3); for photograph of
skull, see Plate 2_d_, and Plate 4_e_.

_Comparisons._--From _B. t. taylori_, _B. t. fuliginatus_ differs in:
dorsum slightly darker than in darkest _taylori_; tail densely haired,
bicolored rather than unicolored; belly sooty to grayish rather than
grayish to whitish; forefeet and hind feet sooty to grayish rather than
flesh-colored; incisive foramina less bowed laterally, more nearly
straight; interparietal compressed anteroposteriorly, less
diamond-shaped.

From _B. t. paulus_, _B. t. fuliginatus_ differs in: dorsum dusky to
blackish rather than fawn color; belly sooty to grayish rather than
buffy to whitish-gray; forefeet and hind feet sooty to grayish rather
than whitish; zygoma more nearly forming a right angle with rostrum or
skull, less tapered anteriorly; anterior part of jugal possessing
ventral projection; jugal extending nearly to lacrimal on posterior
surface of maxillary part of zygoma.

From _B. t. analogous_, _B. t. fuliginatus_ differs in: mid-dorsal
region blacker, less brownish; tail distinctly bicolored rather than
unicolored to faintly bicolored; incisive foramina not constricted
medially; presphenoid broader (at narrowest point); jugal differs much
the same as it does from _paulus_; nasals anteriorly truncate instead of
rounded.

_Remarks._--Dalquest (1953:155-157) and Booth (1957:15) assigned all of
the pygmy mice that they examined from the state of San Luis Potosí to
_B. t. taylori_. Examination of all of the material that was available
to Dalquest, plus additional specimens at the University of Kansas
Museum of Natural History, reveals that there are three subspecies in
San Luis Potosí. _B. t. taylori_ occurs in the eastern part of the State
at lower altitudes; _B. t. analogous_ occurs to the southeast at higher
altitudes; _B. t. fuliginatus_ occurs in the northeastern part of the
State in the Sierra Madre Oriental.

Specimens obtained from Ebano, Pujal, and Tamuín, representative of _B.
t. taylori_, are much paler on the belly and on the ventral surface of
the forefeet and hind feet than are specimens from Ciudad del Maíz,
representative of _B. t. fuliginatus_. The tail in _B. t. taylori_ is
nearly unicolored and less hairy than in the paratypical series of
_fuliginatus_. Specimens from 4 km. NE Ciudad Valles are nearly
intermediate in color of the belly, dorsum, forefeet and hind feet, and
tail, between the palest mice from the coastal plain and the darker mice
in the mountains of the northeastern part of the State (specimens from
El Salto average paler, however, than the type and paratypes). These
specimens seem to be intergrades between _B. t. taylori_ to the east on
the coastal plain and _fuliginatus_ to the northwest in the mountains.
It seems best to refer the mice from 4 km. N Ciudad Valles to _B. t.
taylori_ on the basis of the average of external and cranial characters.
Specimens from 6 mi. SW San Gerónimo, Coahuila, also referred to _B. t.
taylori_, resemble in color the mice from 4 km. N Ciudad Valles. When
more specimens are obtained from the front range of the Sierra Madre
Oriental, at lower altitudes, the manner in which these two subspecies
intergrade with one another will be better understood. At present,
populations from higher altitudes in the mountains seem to represent a
dark subspecies; populations from the coastal plain represent a pale
subspecies, and those from the lower slopes and high valleys seemingly
are intergrades. _B. t. fuliginatus_ occurs in a somewhat limited strip
of chernozem soil (or suelos negros of Tamayo, 1949: Carta de Suelos).
The populations occurring at lower altitudes on the coastal plain are on
generally paler soils.

_Specimens examined._--Total 39, all from the Republic of México, as
follows: SAN LUIS POTOSÍ: El Salto, 24 Mus. Nat. Hist., Louisiana State
Univ., 7 Amer. Mus. Nat. Hist.; type locality, 8 (including the type).

_Marginal records._--See specimens examined.


=Baiomys taylori paulus= (J. A. Allen)

    _Peromyscus paulus_, J. A. Allen, Bull. Amer. Mus. Nat. Hist.,
       19:598, November 12, 1903; Elliot, Field Columb. Mus. Publ.,
       105(6): 136, July 1, 1905.

    _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, 2:402, March 21, 1941 (part); Goldman, Smith, Miscl. Coll.,
       115:373, July 31, 1951 (part); Hall and Kelson, Univ. Kansas Publs.,
       Mus. Nat. Hist., 26:367, December 15, 1952; Goodwin, Bull. Amer.
       Mus. Nat. Hist., 102:318, August 31, 1953; Miller and Kellogg, Bull.
       U. S. Nat. Mus., 205:511, March 3, 1955 (part); Packard, Proc. Biol.
       Soc. Washington, 71:17, April 11, 1958; Packard, Jour. Mamm.,
       40:146, February 20, 1959; Hall and Kelson, The Mammals of North
       America, 2:659, March 31, 1959 (part).

    [_Peromyscus_] _paulus_, Elliot, Field Columb, Mus. Publ.,
       95(4):136, July 15, 1904.

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

    _Peromyscus musculus_ [_musculus_], Osgood, N. Amer. Fauna, 28:256,
       April 17, 1909 (part).

    _Baiomys taylori_ [= _paulus_], Twente and Baker, Jour. Mamm.,
       32:121, February 15, 1951.

    _Baiomys musculus musculus_, Goldman, Smith. Miscl. Coll., 115:336,
       July 31, 1951 (part).

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

_Type._--Adult male, skin and skull; No. 21165, American Museum of
Natural History; Río Sestín, Durango, Republic of México; obtained on
April 15, 1903, by J. H. Batty, original number 455.

_Range._--Central Chihuahua south through Durango (west to eastern edge
of Sierra Madre Occidental), to Zacatecas and Aguascalientes, thence
west into northern and northwestern Jalisco, see Figure 11. Zonal range:
Lower Sonoran, approximately the Chihuahua Desert Biotic Province of
Goldman and Moore (1945:349). Occurs from 4000 feet 2 mi. ESE Tequila,
Jalisco, up to 6700 feet 2 mi. W Miñaca, Chihuahua.

_Diagnosis._--Size medium to small for the species; dorsum Buffy Brown
to fawn color; dorsal ground color of unworn pelage of adults varying
from Buffy Brown in darkest series (especially those from higher
altitudes) to Avellaneous with grayish overtones in palest series; worn
pelage in mid-dorsal region of adults fawn to grayish; terminal parts of
individual hairs buffy, gray basally; guard hairs on dorsum
black-tipped, grayish basally; belly Light Gull Gray, distal half of
hairs white, proximal half Neutral Gray; hairs in region of throat and
chin white to base (some specimens with faint buffy overtones); forefeet
dusky below, whitish above; hind feet whitish above, ventral surface
whitish to dusky; dorsal and lateral vibrissae black, other vibrissae
white. Average and extreme measurements of six adults from the type
locality are as follows: total length, 109 (106-117); length of tail,
44.5 (43-48); length of body, 63 (57-69); length of hind foot, 13.1
(12.7-14.0); occipitonasal length, 17.5 (17.4-18.0); zygomatic breadth,
9.3 (9.1-9.5); postpalatal length, 6.6 (6.2-6.9); least interorbital
breadth, 3.5 (3.4-3.6); length of incisive foramina, 3.8 (3.6-4.1);
length of rostrum, 5.9 (5.7-6.0); breadth of braincase, 8.6 (8.5-8.8);
depth of cranium, 6.6 (6.2-6.9); alveolar length of maxillary tooth-row,
3.2 (3.1-3.4); for photographs of the skull, see Plate 2_e_ and Plate
4_f_.

_Comparisons._--For comparisons with _B. t. allex_, _B. t. canutus_, _B.
t. ater_, and _B. t. taylori_, see accounts of those subspecies. From
_B. t. analogous_, _B. t. paulus_ differs as follows: dorsal color paler
having more reddish-brown than blackish-brown tones; venter whitish to
buffy, instead of gray to light-gray; tail bicolored (not unicolored),
usually having more hairs; hind feet white (not sooty) above. Cranially,
_B. t. paulus_ differs from _B. t. analogous_ in: skull slightly smaller
in all dimensions; maxillary part of zygoma narrowing and forming
oblique angle rather than a near right angle with rostrum; anterior
incisive foramina constricted posteriorly; tips of nasals truncate (less
rounded).

_Remarks._--J. A. Allen (1903:599) correctly pointed out that young
specimens, in first pelage, were gray brown; young adults were darker
and more varied with some blackish; adults and old adults were buffy to
grayish. The change in color of pelage with increasing age is more
pronounced in _paulus_ than in other subspecies of _B. taylori_. Of two
males collected on April 12, 1949, one, an adult, is buffy brown, and
the other, an old adult with worn pelage, is grayish-brown. In mice in
the earlier stages of adulthood, underfur of the dorsum is buffy at the
tips and gray basally. With increased wear, the buffy tip is lost.
Consequently, mice in the later stages of adulthood are grayish.

_B. t. paulus_ intergrades with _ater_ to the north in Chihuahua (see
account of that subspecies), with _analogous_ to the south in Jalisco,
and with _allex_ (see account of that subspecies) to the southwest in
Nayarit and Jalisco. The zone of intergradation between _paulus_ and
_analogous_ in Jalisco approximately borders the Río Grande de Santiago
from the western part of the State to the northwest shore of Lago de
Chapala. Nineteen specimens from 2 mi. WNW Lagos de Moreno in northwest
Jalisco seem to be intermediate between _paulus_ and _analogous_ in
color, averaging slightly grayer than typical _paulus_. The series of 19
is referable to _paulus_ on the basis of cranial characters.

A series of 34 specimens from 3 mi. W La Venta, Jalisco (referable to
_paulus_), is indistinguishable in color of pelage from two series of
_paulus_ from 5 mi. N Durango, and from 8 mi. NE of Durango, except that
the antiplantar surfaces of the hind feet are sooty as in _analogous_.
Seemingly, features of color mentioned above as diagnostic of the two
subspecies are either present or absent and there is no tendency toward
intermediacy in color in the population from 3 mi. W La Venta.

The Río Grande de Santiago may have acted in the past as a physical
barrier reducing gene flow between _allex_ and _paulus_ and in
separating completely the two populations for limited periods.

_Specimens examined._--Total 176, all from the Republic of México and
distributed as follows: CHIHUAHUA: Rancho Sanignacio, 4 mi. S, 1 mi. W
Santo Tomás, 1; El Rosario, 6700 ft., 1; 2 mi. W Miñaca, 6900 ft., 11;
Balleza, 1[50]. DURANGO: Rosario, 1[51]; type locality, 14[51] (including
the type); _San Gabriel_, 2[51]; _Rancho Santuario_, 2[51]; 1 mi. N
Chorro, 6450 ft., 1; _8 mi. NE Durango_, 6200 ft., 2; 5 mi. N Durango,
6400 ft., 2. ZACATECAS: Valparaíso, 6500 ft., 10[50]. AGUASCALIENTES: _18
mi. W, 2 mi. S Aguascalientes_, 6000 ft., 1; 16 mi. S Aguascalientes,
5[52]. JALISCO: 1 mi. NE Villa Hidalgo, 6500 ft., 1; 2 mi. WNW Lagos de
Moreno, 6370 ft., 19; _2 mi. ESE Tequila_, 4000 ft., 11; _3 mi. W La
Venta_, 33, 1[53]; _12 mi. W Guadalajara_, 3[54]; _Atemajac_, 12[50]; 4 mi.
W Guadalajara, 5100 ft., 3; _2 mi. N, 1/2 mi. W Guadalajara_, 11; 2 mi.
NW Magdalena, 4500 ft., 7[50]; _1 mi. N Tala_, 4400 ft., 3; 3 mi. W Tala,
4300 ft., 18.

_Marginal records._--CHIHUAHUA: Rancho Sanignacio, 4 mi. S, 1 mi. W
Santo Tomás; El Rosario; Balleza. DURANGO: Rosario, 6700 ft.; 1 mi. E
Zarca (Blossom and Burt, 1942:1); 1 mi. N Chorro, 6450 ft. ZACATECAS:
Valparaíso, 6500 ft. AGUASCALIENTES: 1 mi. N Chicalote (Blossom and
Burt, 1942:4). JALISCO: 2 mi. WNW Lagos de Moreno, 6370 ft.; 4 mi. W
Guadalajara, 5100 ft.; 3 mi. W Tala, 4300 ft.; 2 mi. NW Magdalena, 4500
ft. DURANGO: 5 mi. N Durango, 6400 ft.; type locality. CHIHUAHUA: 2 mi.
W Miñaca, 6900 ft.

[50] United States National Museum (Biol. Surv. Collections).

[51] American Museum of Natural History.

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

[53] The Museum, Michigan State Univ.

[54] Univ. Michigan, Museum of Zoology.


=Baiomys taylori subater= (V. Bailey)

    _Peromyscus taylori subater_, V. Bailey, N. Amer. Fauna, 25:102,
       October 24, 1905; Lyon and Osgood, Bull. U. S. Nat. Mus., 62:139,
       January 15, 1909; Osgood, N. Amer. Fauna, 28:255, April 17, 1909;
       Elliot, Check-List Mamm. N. Amer. Continent, West Indies and
       Neighboring Seas, Suppl., Amer. Mus. Nat. Hist, p. 44, January 8,
       1917.

    _Baiomys taylori subater_, Miller, Bull. U. S. Nat. Mus., 79:136,
       December 31, 1912; Miller, Bull. U. S. Nat. Mus., 128:317, April 29,
       1924; Anthony, Field Book of North American Mammals, p. 348, 1928;
       Baker, Jour. Mamm., 21:223, May 14, 1940; Ellerman, The Families and
       Genera of Living Rodents, 2:402, March 21, 1941; Blair, Jour. Mamm.,
       22:378, November 14, 1941; Poole and Schantz, Bull. U. S. Nat. Mus.,
       178:259, March 6, 1942; Blair, Jour. Mamm., 23:196, May 14, 1942;
       Blair and Blossom, Contrib. Lab. Vert. Biol., Univ. Michigan, 40:1,
       March, 1948; Miller and Kellogg, Bull. U. S. Nat. Mus., 205:511,
       March 3, 1955; Hall and Kelson, The Mammals of North America, 2:659,
       March 31, 1959.

    _Baiomys taylori_ [= _subater_], Taylor and Davis, Texas Game, Fish
       and Oyster Comm. Bull., 27:56, August, 1947 (part).

_Type._--Subadult female, skin and skull; No. 32616/44539 U. S. Nat.
Mus. (Biol. Surv. Coll.); Bernard Creek, near Columbia, Brazoria County,
Texas; obtained on February 25, 1892, by W. Lloyd, original number 1122.

_Range._--Southeastern Texas, north of Matagorda Bay west to Lavaca
County, north to Brazos and Walker counties thence east to Jefferson
County, see Figure 11. Occurs from near sea level in Brazoria and
Galveston counties, up to 500 feet in western part of range. Zonal
range: Humid division of lower Austral (the western part of the
Austroriparian Biotic Province of Dice, 1943:18-21).

_Diagnosis._--Size medium to large for the species; mid-dorsal region
Clove Brown (sooty in freshly captured specimens); some parts of
mid-dorsal region all blackish; individual guard hairs of dorsum
black-tipped, Deep Neutral Gray basally; underfur black-tipped with
subterminal band of light buff, Neutral Gray at base; belly
grayish-white, laterally Isabella Color; distal three-fourths of hairs
in region of throat and chin white, proximal fourth light gray; in
median region of belly distal half of individual hairs white, proximal
half dark gray; vibrissae in most specimens black to base. Average and
extreme cranial measurements of six adults from 7 mi. S La Belle are as
follows: occipitonasal length, 18.9 (17.5-19.4); zygomatic breadth, 9.6
(9.1-9.9); postpalatal length, 6.8 (6.2-7.2); least interorbital
breadth, 3.7 (3.4-3.9); length of incisive foramina, 4.0 (3.6-4.2);
length of rostrum, 6.5 (6.1-6.8); breadth of braincase, 8.7 (8.3-8.9);
depth of cranium, 6.7 (6.6-6.8); alveolar length of maxillary tooth-row,
3.1 (2.9-3.2). Average and extreme external measurements of four adults
from Richmond are as follows: total length, 111.5 (108-118); length of
tail vertebrae, 43.5 (41-47); length of body, 68 (67-71); length of hind
foot, 14 (13-15); for photographs of the skull, see Plate 2_f_, and
Plate 4_g_.

_Comparisons._--Because _B. t. subater_ intergrades only with _B. t.
taylori_ to the south and west, _subater_ is compared only with
_taylori_. Young adults of both subspecies in unworn pelage show best
the colors that differentiate the two subspecies. Old adults of
_subater_ in worn pelage appear grayish, resembling _taylori_, and at
that age, only certain cranial characters are of taxonomic use.
Cranially, _subater_ differs from _taylori_ in: presphenoid not shaped
like an hour-glass; parapterygoid processes thicker medially;
interparietal diamond-shaped instead of elongated and compressed. Skull
slightly larger in most measurements.


    [Illustration: PLATE 1

    Photographs of skulls in dorsal view of _Baiomys_. × 2.

    _a._ _B. m. brunneus_, [F] ad., 10834, AMNH, Jalapa, Veracruz.
    _b._ _B. m. grisescens_, [F] ad., 257080, USNM, Comayabuela, Honduras.
    _c._ _B. m. handleyi_, [F] ad., 275597, USNM, Sacapulas, Guatemala.
    _d._ _B. m. infernatis_, [F] ad., 91499, MZUM, Teotitlán, Oaxaca.
    _e._ _B. m. musculus_, [F] ad., 45462, USNM, Colima, Colima.
    _f._ _B. m. nigrescens_, [M] ad., 76834, USNM, Comitán, Chiapas.
    _g._ _B. m. pallidus_, [F] ad., 4802, Texas A & M, Axochiapán, Morelos.
    _h._ _B. m. pullus_, [F] ad., 71608, KU, 8 mi. S Condega, Nicaragua.
    _i._ _B. t. allex_, [F] ad., 45453, USNM, Colima, Colima.]


    [Illustration: PLATE 2

    Photographs of skulls (_a-g_) in dorsal view of _Baiomys_. × 2.

    _a._ _B. t. analogous_, [F] ad., 120265, USNM, Zamora, Michoacán.
    _b._ _B. t. ater_, [F] ad., 15056, UI, 1-1/2 mi. ENE Greaterville,
          Arizona.
    _c._ _B. t. canutus_, [F] ad., 62076, KU, 1 mi. S Pericos, Sinaloa.
    _d._ _B. t. fuliginatus_, [F] ad., 36771, KU, type locality.
    _e._ _B. t. paulus_, [F] ad., 40032, KU, 18 mi. W, 2 mi. S
          Aguascalientes.
    _f._ _B. t. subater_, [F] ad., 44543, USNM, type locality.
    _g._ _B. t. taylori_, [F] ad., 57944, KU, 5 mi. E San Antonio, Texas.
    _h._ Photo. of captive [M] _B. t. taylori_, 25 mi. E Austin, Texas.
    × 1.]


    [Illustration: PLATE 3

    Photographs of skulls in ventral view of _Baiomys_. × 2.

    _a._ _B. m. brunneus_, [F] ad., 10834, AMNH, Jalapa, Veracruz.
    _b._ _B. m. grisescens_, [F] ad., 257080, USNM, Comayabuela, Honduras.
    _c._ _B. m. handleyi_, [F] ad., 275597, USNM, Sacapulas, Guatemala.
    _d._ _B. m. infernatis_, [F] ad., 91499, MZUM, Teotitlán, Oaxaca.
    _e._ _B. m. musculus_, [F] ad., 45462, USNM, Colima, Colima.
    _f._ _B. m. nigrescens_, [M] ad., 76834, USNM, Comitán, Chiapas.
    _g._ _B. m. pallidus_, [F] ad., 4802, Texas A & M, Axochiapán, Morelos.
    _h._ _B. m. pullus_, [F] ad., 71608, KU, 8 mi. S Condega, Nicaragua.]


    [Illustration: PLATE 4

    Photographs of skulls in ventral view of _Baiomys_. × 2.

    _a._ _B. t. allex_, [F] ad., 45453, USNM, Colima, Colima.
    _b._ _B. t. analogous_, [F] ad., 120265, USNM, Zamora, Michoacán.
    _c._ _B. t. ater_, [F] ad., 15056, UI, 1 mi. ENE Greaterville, Arizona.
    _d._ _B. t. canutus_, [F] ad., 62076, KU, 1 mi. S Pericos, Sinaloa
    _e._ _B. t. fuliginatus_, [F] ad., 36771, KU, type locality.
    _f._ _B. t. paulus_, [F] ad., 40032, KU, 18 mi. W, 2 mi. S
          Aguascalientes.
    _g._ _B. t. subater_, [F] ad., 44543, USNM, type locality.
    _h._ _B. t. taylori_, [F] ad., 57944, KU, 5 mi. E San Antonio, Texas.]

_Remarks._--This subspecies retains its chief diagnostic character,
blackish mid-dorsal region, throughout nearly all parts of its range.
Specimens from the general area of Matagorda Bay and Lavaca County grade
into _taylori_ in characters of color and crania. The Colorado and
Brazos rivers seemingly serve as barriers reducing gene flow between
_taylori_ and _subater_. These rivers may well have been important
factors in the origin and the limitation of these two seemingly
closely-related subspecies.

_Baiomys taylori subater_ is not differentiated in color of pelage and
characters of crania from _B. t. taylori_ to the same degree that _B. t.
paulus_ is differentiated from _B. t. analogous_, or that _B. t.
taylori_ is differentiated from several of the other subspecies of
_Baiomys taylori_. _B. t. subater_ probably is a more recent occupant of
the area in which it now lives than is the case with any other one of
the subspecies of _taylori_. Sufficient time probably has not elapsed to
allow for formation of more distinctive phenotypic patterns.

_Specimens examined._--Total 65, all from TEXAS and distributed as
follows: _Brazos County_: 1/2 mi. NW College Station, 1[55]; _3 mi. W
College Station_, _1 mi. W Easterwood Airport_, 1[55]; _College Station_,
1[55]. _Walker County_: Huntsville, 1[55]. _Hardin County_: Sour Lake,
1[57]. _Jefferson County_: 7 mi. S Labelle, 10. _Harris County_: 6 mi. NE
Crosby, 1[56]. _Colorado County_: _10 mi. N Eagle Lake_, 1[55]; _9 mi. N
Eagle Lake_, 1[55]; 2 mi. W Eagle Lake, 1; _Eagle Lake_, 1[55], 5. _Fort
Bend County_: Richmond, 4[57]. _Galveston County_: _Texas City_, 6[58];
Virginia Point, 1[57]. _Brazoria County_: _Austin Bayou near Alvin_,
2[57]; 14 mi. SSE Alvin, 2[59]; type locality, 7[57] (including the type).
_Lavaca County_: 4 mi. W Hallettsville, 1[55]; _1 mi. SW Hallettsville_,
3[55]; _13.7 mi. SW Hallettsville_, 2[55]; 4 mi. NE Yoakum, 11.

_Marginal records._--TEXAS: Huntsville; Sour Lake; 7 mi. S La Belle;
Virginia Point; 14 mi. SSE Alvin; type locality; 4 mi. NE Yoakum; 4 mi.
W Hallettsville; 1/2 mi. NW College Station.

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

[56] Carnegie Museum.

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

[58] Los Angeles County Museum.

[59] American Museum of Natural History.


=Baiomys taylori taylori= (Thomas)

    _Hesperomys_ (_Vesperimus_) _taylori_ Thomas, Ann. Mag. Nat. Hist.,
       ser. 5, 19:66, January, 1887.

    _Baiomys taylori_ [_taylori_], Mearns, Bull. U. S. Nat. Mus.,
       56:381, April 13, 1907; Stickel and Stickel, Jour. Mamm., 30:141,
       May 23, 1949.

    Baiomys taylori taylori, Miller, Bull. U. S. Nat. Mus., 79:136,
       December 31, 1912; Miller, Bull. U. S. Nat. Mus., 128:317, April 29,
       1924; Anthony, Field Book of North American Mammals, p. 327, 1928;
       Ellerman, The Families and Genera of Living Rodents, 2:402, March
       21, 1941; Taylor and Davis, Texas Game, Fish and Oyster Comm. Bull.,
       27:56, August, 1947 (part); Blair, Texas Jour. Sci., 2:104, March
       31, 1950; Goldman, Smith. Miscl. Coll., 115:373, 426, July 31,
       1951; Baker, Univ. Kansas Publs., Mus. Nat. Hist., 5:212, December
       15, 1951; Blair, Texas Jour. Sci., 4:242, June 30, 1952; Hooper,
       Occas. Papers, Univ. Michigan, Mus. Zool., 544:7, March 25, 1953;
       Dalquest, Louisiana State Univ. Studies (Biol. Sci. Ser.), 1:155,
       December 28, 1953 (part); Blair, Adv. in Genetics, 5:10, January 27,
       1954; Miller and Kellogg, Bull. U. S. Nat. Mus., 205:511, March 3,
       1955; Baker, Univ. Kansas Publs., Mus. Nat. Hist., 9:273, June 15,
       1956; Packard, Proc. Biol. Soc. Washington, 71:17, April 11, 1958;
       Hall and Kelson, The Mammals of North America, 2:659, March 31, 1959
       (part).

    _Cricetus_ (_Vesperimus_) _taylori_, Thomas, Proc. Zool. Soc.
       London, 68:446, November 20, 1888.

    _Sitomys taylori_, Merriam, Proc. Biol. Soc. Washington, 7:170,
       September 29, 1892.

    _Sitomys_ (_Baiomys_) _taylori_, True, Proc. U. S. Nat. Mus.,
       16(972):758, February 7, 1894; J. A. Allen, Bull. Amer. Mus. Nat.
       Hist., 6:181, May 31, 1894.

    _S._ [_itomys_] _taylori_, Rhoads, Proc. Acad. Nat. Sci.
       Philadelphia, 46:256, October, 1894.

    _Peromyscus_ (_Baiomys_) _taylori_, J. A. Allen, Bull. Amer. Mus.
       Nat. Hist., 8:65, April 22, 1896.

    [_Peromyscus_] _taylori_, Trouessart, Cat. Mamm., 1:517, 1898.

    _Peromyscus taylori_ [_taylori_], Elliot, Field Columb. Mus. Publ.,
       105(4):135, July 1, 1905; V. Bailey, N. Amer. Fauna, 25:101, October
       24, 1905; Elliot, Field Columb. Mus. Publ., 115(8):203, 1907;
       Osgood, N. Amer. Fauna, 28:253, April 17, 1909.

_Type._--Adult male, skin and skull; No. 87.11.24.1, British Museum,
Natural History; San Diego, Duval County, Texas; obtained by William
Taylor.

_Range._--North-central to southeastern Texas, excluding the coastal
plain north of the region of Matagorda Bay, thence south into the
southern part of Tamaulipas and west into Coahuila and Nuevo León, see
Figure 11. Occurs from near sea level in Texas up to 1500 feet in
Coahuila. Zonal range: mostly Lower Austral (in México and southeastern
half of Texas, the Tamaulipas Biotic Province of Goldman and Moore,
1945:349, and Blair, 1952:230).

_Diagnosis._--Size medium for the species; dorsum grayish in freshly
taken specimens to Hair Brown in preserved specimens; individual guard
hairs of dorsum black-tipped, grayish basally, underfur black-tipped
with a subterminal band of olive-buff; sides of body pale-grayish near
venter, individual hairs buffy proximally, grayish basally; belly pale
grayish, individual hairs white-tipped, Pale Neutral Gray basally;
throat and chin colored as is belly; forefeet and hind feet sooty-gray
dorsally, sparsely-haired ventrally, thus appearing flesh-colored; tail
unicolored gray to sooty-gray. Average and extreme cranial measurements
of 22 adults from 6 mi. SW San Gerónimo, Coahuila, are as follows:
occipitonasal length, 18.0 (17.4-19.0); zygomatic breadth, 9.6
(9.2-10.2); postpalatal length, 6.5 (5.9-7.1); least interorbital
breadth, 3.6 (3.3-3.8); length of incisive foramina, 4.0 (3.6-4.3);
length of rostrum, 6.1 (5.7-6.7); breadth of brain case, 8.8 (8.5-9.1);
depth of cranium, 6.5 (6.0-7.0); alveolar length of maxillary tooth-row,
3.1 (3.0-3.3). Average and extreme external measurements of 19 adults
from 6 mi. SW San Gerónimo are as follows: total length, 102.2 (95-115);
length of tail vertebrae, 39.4 (21-46); length of body, 62.8 (53-76);
length of hind foot, 14.0 (12-15); length of ear from notch, 10.7
(10-12); for photographs of skull, see Plate 2_g_, and Plate 4_h_.

_Comparisons._--For comparisons with _B. t. subater_, _B. t. analogous_,
and _B. t. fuliginatus_, see accounts of those subspecies. From _B. t.
paulus_, found to the southwest, _B. t. taylori_ differs as follows:
dorsum grayish rather than fawn-colored; hairs on dorsal parts of
forefeet and hind feet sooty-gray (not white to white-brown); venter
gray to Light Drab-Gray, rather than whitish with gray overtones; tail
unicolored instead of bicolored; skull averaging slightly larger
over-all; maxillary part of zygoma forms right angle with rostrum rather
than obtuse angle; incisive foramina extending posteriorly to anterior
plane of first upper molars instead of to a transverse plane at middle
of right and left first upper molars; bullae less inflated; interorbital
region broader relative to length of skull; rostrum sloping gently from
frontonasal suture to anterior tip of nasals rather than declining
abruptly from frontonasal suture to anterior tip of nasals.

_Remarks._--The geographic range of _taylori_ is relatively large, and
the subspecies is locally variable. Nevertheless, none of the external
and cranial measurements of specimens assigned to this subspecies
differs significantly from the corresponding measurements of material
from the type locality and adjacent areas in southeastern Texas. In
southeastern Texas, south of the Guadalupe River, south to the coastal
plain of Tamaulipas, this subspecies differs in color (being paler) from
_B. t. subater_ with which _taylori_ might be confused. The foothills of
the Sierra Madre Oriental in western Tamaulipas, north through Nuevo
León and Coahuila, seem to mark the southwestern limit of the range
assignable to _taylori_.

On December 27, 1958, a specimen, KU 81552, was obtained 3 mi. N Bowie,
Montague County, Texas. This record station extends the known range of
_B. taylori_ 65 miles northward from the previous northernmost locality,
listed by Hunsaker, Raun, and Swindells (1959:447). Two specimens, KU
81553 and 81554, were collected by the author 2 mi. NE Cedar Hill,
Dallas County, Texas, on October 31, 1958. These two specimens, plus the
single specimen from Bowie County are all paler with more buffy bellies
than either _B. t. taylori_ or _B. t. subater_. They may represent an
incipient subspecies. I tentatively assign them to _B. t. taylori_
because of the pale rather than dark (like _B. t. subater_) pelage.
Additional specimens are needed from these areas and from the hiatus
between the ranges of _B. t. taylori_ and _B. t. subater_ the better to
understand the manner in which these two subspecies intergrade.

Among named subspecies of _Baiomys taylori_, _B. t. taylori_ most
closely resembles _B. t. subater_ to the north in Texas. Nine specimens
examined from Yoakum are intergrades between _taylori_ and _subater_.
These specimens have the sooty dorsal color of _subater_, but ventrally
are inseparable from topotypes of _taylori_. In length of body and
tail, specimens from Yoakum are like _subater_, but in length of hind
foot, they are intermediate between the two subspecies. Cranially, they
are like _subater_. When all characters are considered, the specimens
are best referred to _subater_. Bailey (1905:103) suggested that
specimens from the southern part of the range, which he ascribed to
_subater_, tended to a more grayish color than topotypes of _subater_,
therefore, grading into _taylori_. The zone of intergradation runs from
Matagorda Bay northwest through Lavaca County, thence north to the
Colorado River, and closely follows the boundary between the Lower
Austral and Humid Division of Lower Austral Life-zone as plotted by
Bailey (_loc. cit._). Findley (1955:44) pointed out that where two
life-zones meet, the resulting populations of shrews are mostly
intergrades. Such is the case between these two subspecies of _Baiomys
taylori_ in an area where life-zones might seem less important than in
the mountainous west.

In the southern part of the range of _taylori_, intergradation occurs
between _B. t. taylori_ in western Tamaulipas and _B. t. fuliginatus_ in
the mountains of San Luis Potosí.

Dalquest (1953:156) found no indication of intergradation between the
two species, _B. taylori_ and _B. musculus_, in San Luis Potosí. After
examination of specimens from San Luis Potosí, I am in agreement that
they are all referable to the species _taylori_.

_Specimens examined._--Total 435. TEXAS: _Montague County_: 3 mi. N
Bowie, 1. _Dallas County_: 2 mi. NE Cedar Hill, 2. _Travis County_:
8 mi. NW Austin, 2[60]; _Austin_, 2[60]; _4 mi. E Austin_, 4[60];
_5 mi. E Austin_, 3[60]; _6 mi. E Austin_, 16[60], 1; _7 mi. E Austin_,
1[60]; _15 mi. E Austin_, 1[60]; _4 mi. S Austin_, 1[60]. _Bastrop
County_: 25 mi. E Austin, 2. _Kendall County_: Boerne, 1[61].
_Bexar County_: _1 mi. N Randolph Field_, 3[64]; _5 mi. ENE_
(_on U. S. Highway 81_) _San Antonio_, 1; _3 mi. NE San Antonio_, 1;
San Antonio, 26[61], 11[62], 1[63]; _5 mi. E San Antonio_, 11;
_4-1/2 mi. E Sayers_, 3. _Gonzales County_: 7 mi. S Luling, 2[60].
_Wilson County: 4 mi. W LaVernia_, 3; 12 mi. W Floresville, 1.
_Atascosa County_: 9 mi. SW Somerset, 1. _Goliad County_: 8 mi.
NE Goliad, 1[60]. _Bee County_: Beeville, 1[61]. _Aransas County_:
Aransas (Wildlife) Refuge, 1[65]; _5 mi. E Copana Bay_, 1[65];
_4.6 mi. NE Rockport_, 5[60]; _4.5 mi. NW Rockport_, 2[60]; 3 mi. N,
2 mi. E Rockport, 4; _Rockport_, 1[60], 1[61], 1[63]; _1-1/2 mi.
SW Rockport_, 1[60]; _2 mi. SW Rockport_, 2[60]; _13.4 mi. SW Rockport_,
1[60]; _14 mi. SW Rockport_, 1. _San Patricio County_: Welder Wildlife
Refuge, 7. _Duval County_: type locality, 2[61], 1[66]. _Nueces County_:
Corpus Christi (south Nueces Bay), 1[64] (Cleveland Mus. Coll.). _Kleberg
County_: 2 mi. S Riviera, 3[65]. _Brooks County_: 3 mi. S Falfurrias,
2[65]. _Hidalgo County_: 6 mi. S McAllen, 17[60]. _Willacy County_: 28 mi.
E Raymondville, 10[65]. _Cameron County_: Brownsville, 31[61], 23[62],
5[64]. COAHUILA: 6 mi. SW San Gerónimo, 32. NUEVO LEÓN: Santa Catarina,
1[61]; 14 mi. N Monterrey, 1950 ft., 2[67]; Monterrey, 1[61]; 20 km. N
General Terán, 3[64]. TAMAULIPAS: _Near Headwaters Río Sabinas, 8 km. W,
10 km. N El Encino_, 400 ft., 1; Camargo, 5[61]; Charco Escondido, 20 mi.
S Reynosa, 3[67]; Matomoras, 5[61]; _Ejido Santa Isabel, 2 km. W
Inter-American Highway_, 2000 ft., 7; Hidaglo, 7[61]; _Hda. Station
Engracia_, 4[63]; 4 mi. N La Pesca, 1; 29 mi. N Ciudad Victoria, 1[67];
Ciudad Victoria, 6[61], 3; Jaumavé, 2400 ft., 6[64], 10; Sierra de
Tamaulipas, 3[64]; _25 mi. N El Manté, 3 km. W Inter-American Highway_
(_on Rancho Pano Ayuctle_), 300 ft., 4; _6 mi. N Gomez Farias_ (_on
Rancho Pano Ayuctle_), 1; _5 mi. NE Gomez Farias_, 12[64], 1[62]; 70 km.
(by highway) S Ciudad Victoria, 2 km. W El Carrizo, 5[62], 2; Antigua
Morelos, 5[64]; _6 mi. N, 6 mi. W Altamira_, 31; _5 mi. N, 5 mi. W
Altamira_, 4; _Alta Mira_ (_Altamira_), 2[61]; 1 mi. S Altamira, 6; _10
mi. NW Tampico_, 1. SAN LUIS POTOSÍ: Ebano, 5[68]; _4 km. NE Ciudad
Valles_, 1; Ciudad Valles, 1; _3 km. W Tamuín_, 1[68]; _Tamuín_, 6[68];
_Pujal_, 300 m., 1[64]. VERACRUZ: Tampico Alto, 50 ft., 1; Potrero Llano,
350 ft., 1; Ozulama, 2; Cerro Azul, 350 ft., 1.

_Marginal Records._--TEXAS: 3 mi. N Bowie; 2 mi. NE Cedar Hill; 25 mi. E
Austin; 7 mi. S Luling; 8 mi. NE Goliad; Aransas (Wildlife) Refuge; 3
mi. N, 2 mi. E Rockport; Corpus Christi (South Nueces Bay); 2 mi. S
Riviera; 28 mi. E Raymondville; Brownsville. TAMAULIPAS: Matomores; 4
mi. N La Pesca; 1 mi. S Altamira. VERACRUZ: Tampico Alto; Ozulama; Cerro
Azul; Potrero Llano. SAN LUIS POTOSÍ: Ciudad Valles. TAMAULIPAS: Antigua
Morelos; 70 km. S Ciudad Victoria, 2 km. W El Carrizo; Jaumavé; Hidalgo.
NUEVO LEÓN: 20 km. N General Terán; Santa Catarina. COAHUILA: 6 mi. SW
San Gerónimo. TEXAS: 9 mi. SW Somerset; Boerne; 8 mi. NW Austin.

[60] Coll. University of Texas.

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

[62] American Museum of Natural History.

[63] Chicago Natural History Museum.

[64] Univ. Michigan, Museum of Zoology.

[65] Texas A & M Coop. Wildlife Res. Coll.

[66] Carnegie Museum.

[67] Univ. California, Mus. Vert. Zool.

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




EVOLUTION AND SPECIATION


The history of the genus dates back to the early late Pliocene, but
morphological change since then has been slight insofar as can be judged
from lower jaws. _Baiomys_ seems to have been relatively conservative
also in types of habitat occupied.

According to Wilson (1937:59), the late Pliocene was a time of decided
expansion of myomorph rodents, more particularly cricetines.
Furthermore, at this time, the climate in the interior basin of
southwestern North America presumably was becoming arid, if we can judge
from the spread of elements of the Madro-Tertiary flora. Axelrod
(1950:266) points out that the drier, continental climate initiated in
the early Tertiary probably had its culmination in middle Pliocene time.
Some floras of early late Pliocene of the southwestern United States
reflect a climate slightly cooler and more moist than the climates of
the middle Pliocene. However, late Pliocene times reflect an arid
climate. The flora of the southwestern interior basin of North America
in early late to late Pliocene was intermediate between the previous
grassland floras of the middle Pliocene and the savannah flora of upper
Pliocene. Axelrod (_loc. cit._) suggests that this intermediate flora of
the interior basin of southwestern North America resulted from the
folding of the Cascades and uplifting of the Sierra Nevada and
Peninsular ranges to the south. The development of these mountains
produced greater aridity to the lee of the mountains, thus accounting
for the grassland-savannah flora. Pygmy mice probably originated in that
time, I judge in México, and moved northward and southward in a
grassland-savannah habitat that seemingly existed as far north as what
is now Meade County, Kansas (where the Sawrock fauna lived). Further
evidence for occupancy of a grassland-savannah habitat by ancestral
pygmy mice stems from the distribution of the living species, _B.
taylori_, that at present occupies territory adjacent to parts of the
Sonoran and Chihuahuan deserts. _B. taylori_ seems to be morphologically
more specialized for life in an arid grassland than was _B.
sawrockensis_.

The geographic range of ancestral pygmy mice possibly extended farther
south in late Pliocene time than the range of _B. musculus_ does now.
Anyhow, _B. sawrockensis_ of the early late Pliocene dwelt in a more
mesic type of habitat than _B. musculus_ does, and such habitat may have
existed from the Pacific lowlands of Central America to the Caribbean
lowlands of northern South America (see Duellman, 1958:136, and Dunn,
1940:156) during late Pliocene times. An ancestral stock of hesperomine
mice, not greatly different from _Baiomys_, may have emigrated from the
North American continent into South America across the continuous land
connection, which Simpson (1950:395) suggests was formed in the
Chapadmalalan age (= Blancan age of North American terminology). The
length of time of interchange of genes between northern and southern
populations of mice across the Central American land connection probably
was brief. Duellman (_op. cit._:129) pointed out that once the
Panamanian portal was closed, the warm counter equatorial current, El
Niño, combined with the uplifting of the Andes, began to produce heavy
rain forests in Central America and northern South America in late
Pliocene or early Pleistocene times. These forests presumably isolated
the stock in North America from that in South America where the latter
probably evolved rapidly into kinds that differed from one another and
from _Baiomys_ in shape of body, type of pelage, and shape of skull.
Internal structures such as hyoid apparatus, auditory ossicles, and
baculum remained almost unchanged, as for example in _Calomys_ now
living in South America. The present resemblance in internal
morphological features between it and _Baiomys_, I judge, reflects
taxonomic relationships more accurately than do shape and conformation
of body and skull that seem to respond more rapidly to external
environmental changes. The cranial characters distinguishing _Baiomys
musculus_ from _Calomys laucha_ are as follows: posterior lacerate
foramina between second, rather than first, upper molars; parapterygoid
fossa shallower; mesopterygoid fossa as wide or wider, instead of
narrower, than parapterygoid processes; burr for attachment of
superficial masseter muscle hypertrophied instead of well-developed. In
other cranial characters studied, the two genera closely resemble each
other. Such similarities of crania between _Calomys_ and _Baiomys_ may
reflect convergence, but the total of internal and external
morphological characters shared, I think reflects true relationships.

_Peromyscus_ has a large number of living and extinct species and
exhibits a wide range of morphological variation, whereas _Baiomys_ has
a small number (7) of species and exhibits a narrow range of
morphological variation. The small number of known species of pygmy mice
suggests their conservatism in elaboration of morphological characters.
Possibly this is because the habitat, or even the ecological niche,
occupied in geological time by these mice was restricted, geographically
and in kind. If the habitat of the pygmy mice oscillated between
savannah and arid grassland, then an hypothesis can be made possibly
accounting for the origin of species of these mice. My idea is that the
geographical distribution of _Baiomys_ today reflects a predilection on
the part of these mice for a relatively uniform warm climate. Therefore,
in the past, in times of warmer continental climate, these mice moved
toward favorable habitat northward from an area in central and northern
México. In cooler periods, the mice moved southward as habitats to the
north became unfavorable.

Dr. W. B. Davis (_in. litt._) informs me that _B. taylori_ was uncommon
in Brazos County, Texas, approximately 15 years ago, and suggests that
the abundance there now of this mouse and my taking it in 1958 northward
nearly to the southern border of Oklahoma reflects a definite movement
northward. Movement in the same direction in late years has been
suggested for the nine-banded armadillo and the hispid cotton rat (Hall,
1959:373) that are associated with warm climates to the south. These
movements possibly reflect only minor fluctuations of climate, but in a
long period of warmth movements northward would be expected to be
pronounced and extensive.

Extinct species of _Baiomys_ may have originated as a result of
extension northward of the geographical range and subsequent retreat
southward of the northern populations, as follows: (1) the range of the
genus moved northward in a warm period; (2) in cooler times, most of the
mice in the north disappeared and only isolated colonies remained in
small patches of remaining habitat still favorable to the mice; (3) the
small populations of isolated pygmy mice after a time changed through
mutations, recombinations and subsequent selection to a degree that
prevented crossbreeding once populations from the south again moved
northward and came in contact with previously isolated stocks; (4) then
competition caused further divergence in morphological characters. Such
an hypothesis would account for the morphological differences between
the extinct _B. kolbi_ and _B. rexroadi_. The extinct _B.
brachygnathus_, presumably a dweller of a xerophytic grassland, may have
had its origin from a _B. minimus_-like stock in the manner outlined.


FORMATION OF THE RECENT SPECIES

The morphological difference between the extinct _B. minimus_ and the
living _B. musculus_ is not great, and musculus seems to be the product
of the _B. sawrockensis-B. minimus_ line of development. Morphological
characters of the parental stock of the two living species, _musculus_
and _taylori_, may have been intermediate between those of _B. minimus_
and those of _B. musculus_. The principal part of the range of _Baiomys_
today is in México, and probably was there through much of Pleistocene
time. Extension northward of the species and retreat southward of those
northern populations of pygmy mice would not only have left isolated
populations in the north, but would have allowed the mice that retreated
south to share a common gene pool. Therefore, populations of pygmy mice
occurring to the south in central México might be expected to maintain a
relatively high degree of heterozygosity in morphological and behavioral
characters. The occurrence of any physical or biotic barrier that would
have separated this homogeneous group would be conducive to speciation.
There is evidence that a barrier occurred in the Pleistocene in central
México sufficient to separate the supposed interbreeding, relatively
homogeneous populations of pygmy mice. According to Sears (1955:529) and
De Terra _et al_. (1949:51), parts of the higher regions in the Valley
of México, and the transverse volcanic zone in central México were
glaciated. On the mountain Ixtaccihuatl, De Terra (_op. cit._:52) found
evidence of four marked advances of ice, from oldest to youngest, as
follows: Salto, ice advanced to 3100 meters; Xopano, ice at 3200-3300
meters; Trancas, ice to 3400 meters; Ayolotepito, ice to 4350 meters.
The Salto advance is correlated by De Terra (_loc. cit._) with the Iowan
glacial period. The advance of ice down the mountain sides in the
transverse volcanic zone was accompanied by cool moist climates or
pluvial periods. Such climates probably altered habitat formerly
suitable for _Baiomys_. There is no record of _Baiomys_ known to me
exceeding 8000 feet in elevation, although the lower edge of the ice on
Ixtaccihuatl is at approximately 15,300 feet (4600 meters, Sears, _loc.
cit._). Presumably, the advance of ice down the mountains forced the
pygmy mice to move to lower altitudes. Pluvial conditions possibly
rendered the habitat even at lower altitudes uninhabitable for the mice,
with the result that none continued to live in the transverse volcanic
zone, but only north and south thereof. Long-continued separation of
these northern and southern segments allowed species formation to occur.
As climatic and habitat conditions became more favorable in central
México, the two species moved back toward each other, and eventually
their geographic ranges overlapped.

An analysis of external and cranial characters of pygmy mice (see Figure
12) reveals that both species are essentially largest to the north and
smallest to the south. There are exceptions to this cline in both
species. For example, _B. taylori analogous_ is a large subspecies; it
lives allopatrically in the southern part of the range of the species.
_B. musculus pallidus_ is not the largest subspecies; it lives
allopatrically in the northern part of the range of the species. In
west-central México, where the two species are sympatric, _B. taylori_
is smaller than elsewhere and _B. musculus_ is larger than elsewhere.
_B. t. analogous_ lives in the mountains of the transverse volcanic zone
in central México. Its large size may be a result of the cooler climate
in the mountains. _B. t. allex_, the smallest subspecies, lives
sympatrically with _B. musculus musculus_ at lower elevations in
west-central México. The small size of _allex_ could be a result of the
warmer climate of the lower elevations. _B. m. pallidus_, at lower
elevations in southern Oaxaca, is smaller than other subspecies of
_musculus_ to the south at higher elevations. _B. m. musculus_ lives at
low elevations along the coast of west-central México. Unlike _B. m.
pallidus_, _B. m. musculus_ is large at lower elevations. It occurs
sympatrically with _B. t. allex_. It is my idea that during the period
of separation, when the two species were evolving, larger subspecies
evolved to the north or at higher altitudes where climates were cooler;
smaller subspecies evolved to the south or at lower elevations; the two
cognate species, _musculus_ and _taylori_, made contact at lower
elevations where individuals of _taylori_ may have been smallest, but
individuals of _musculus_ were not the largest of the species. The
differences, therefore, between the two species in their initial contact
probably were slight. Hybrids, if they occurred, were probably
inviable, sterile, or ill-suited for occupancy of the habitat of either
of the parental stocks. The occurrence of hybrids, therefore, would
result in what geneticists call "gamete wastage," and any further
divergence in the parental stock, either in external characters (size
and shape of body and head), or behavior, useful in recognition of
species, would be favored by natural selection (see Dobzhansky,
1951:225; and Koopman, 1950:147). The two species seem to have diverged
more in external characters where they occur together than in areas
where they live separately (see Figure 12). The two species could be
confused if a sample of adults of _taylori_ from 7 mi. S La Belle,
Jefferson County, Texas, were compared to a sample of adults of
_musculus_ from Tehuantepec, Oaxaca (see Figure 12). No confusion in
species identity would arise, however, if a sample of adults was taken
from the area where the two species live together (see Figure 12). Brown
and Wilson (1956:49) pointed out that where two closely related species
occur together, characters (morphological, ecological, physiological, or
behavioral) of each species are easily distinguished. However, where the
two species are allopatric, the two closely related species so resemble
one another that the species are not easily distinguished. This
phenomenon has been called "character displacement" by Brown and Wilson
(_loc. cit._).

In the area where the two species of pygmy mice occur together, there
seems to be a disparity in numbers between them. Hooper (1952a:91) has
recorded the collection of both _B. musculus_ and _B. taylori_ in a
single trap line. A series of pygmy mice collected from San Gabriel,
Jalisco, contained one _taylori_ and 33 _musculus_; another sample from
La Resolana, Jalisco, had a ratio of 25 _taylori_ to 6 _musculus_. The
disparity in numbers where the two species occur together has been
further substantiated by collections of the University of Kansas.
Possibly this disparity in numbers is a result of interspecific
competition. Hooper (_op. cit._:90) pointed out that where the range of
_B. musculus_ (typical of arid tropical lowlands) meets that of _B.
taylori_ (typical of arid temperate highlands), the two geographic
ranges interdigitate with parts of the range of _musculus_ extending
into the highlands and parts of the range of _taylori_ extending into
the lowlands. In the lowlands, _musculus_ may be better adapted to
environmental conditions and, therefore, more successful in competition
with _taylori_ for available habitat. The reverse situation may exist in
the highlands. Also, the fact that _musculus_ is more of a diurnal
animal than is _taylori_ may account for the difference in numbers of
individuals of the two species taken in trap lines. Many collectors set
their traps in late afternoon or evening and retrieve them in early
morning. Such a schedule might not yield many _musculus_. If
interspecific competition does occur in the area where the two species
occur, any change in habits or microhabitat by either species that would
reduce this competition would be favored by natural selection (see Mayr,
1949:518; Lack, 1944:262-263; and Brown, 1958:154-155). Brown (_op.
cit._:154), as I understand him, pointed out (taking account of Gause's
principle) that when two species having similar ecological valences move
into the same niche in the same locality, one of three things must
eventually happen: (_a_) the two species occupy different geographic
ranges; (_b_) they compete and one is eventually eliminated; (_c_) the
two species, because of differentiation or specialization, exploit
different aspects of the niche. In _Baiomys_, (_c_) seems to apply.
Natural selection probably would favor a continuation of diurnal
activity in _musculus_ and nocturnal activity in _taylori_, thereby
preventing frequent meeting of the two species.


AREAS OF PRESENT DIFFERENTIATION

In both species of _Baiomys_, the most distinct subspecies, _B. t.
allex_ and _B. m. musculus_, occur in the area where the two species are
sympatric. Seven subspecies, or 44 per cent, occur either in or adjacent
to the transverse volcanic zone. This area is the major area of active
differentiation. Incipient subspecies are also evident in these areas. A
secondary area of differentiation is indicated within the range of _B.
musculus_ in Guatemala, El Salvador and Honduras. Three subspecies occur
in this area (_grisescens, handleyi_ and _nigrescens_) and incipient
subspeciation is in evidence there.


ZOOGEOGRAPHIC POSITION

Hooper (1949:25) regards _Baiomys_ as a member of the rodent fauna of
the arid, western Sonoran region, whereas Hershkovitz (1958:609)
suggests that _Baiomys_ is a nearctic-neotropical varicant (a kind that
occurs in contiguous zoogeographic regions without our knowing in which
region the taxon originated). The findings from my study do not
contradict either of the above suggestions. Because of the close
resemblance of _Baiomys_ to certain hesperomine mice of South America,
it is postulated that _Baiomys_, in more primitive form than now,
occurred farther south in past times than it does now. Fossils show that
primitive stocks of the genus in late Pliocene or early Pleistocene
times occurred also north of the present range of the genus. The belt in
west-central México between nearctic and neotropical regions is the
current center of distribution of the genus and probably has been for a
considerable time.

    [Illustration:

    FIG. 12. Averages of the occipitonasal lengths of skulls of adults
       at 19 localities of occurrence (solid symbols) of _Baiomys taylori_,
       and at 17 localities of occurrence (open symbols) of _Baiomys
       musculus_. Note that the occipitonasal length decreases from north
       to south in each of the two species, and that in the region where
       the two species occur together, west-central México, _B. taylori_
       is smallest and _B. musculus_ is largest. Average, extremes, number
       of specimens averaged (in italic type), and name of locality, from
       north to south for each species, are as follows:

    _Baiomys taylori_

    18.0  (17.5-18.6)  _15_, 9-1/2 mi. W New Mexico state line, Ariz.
    18.9  (18.2-19.4)   _6_, 7 mi. S. La Belle, Jefferson Co., Texas.
    18.2  (17.8-18.5)  _10_, San Antonio, Bexar Co., Texas.
    18.2  (18.0-18.5)   _5_, 2 mi. W Miñaca, Chihuahua.
    18.0  (17.6-19.0)  _22_, 6 mi. SW San Gerónimo, Coahuila.
    18.2  (18.1-18.3)   _3_, Ciudad Obregón, Sonora.
    18.1  (17.4-18.5)   _5_, vic. (see p. 649) Durango, Durango.
    18.1  (17.5-18.5)   _9_, Jaumavé, Tamaulipas.
    18.2  (17.7-18.9)  _19_, 15 mi. N Rosario Chelé, Sinaloa.
    17.9  (17.4-18.3)  _27_, vic. (see p. 655) Altamira, Tamaulipas.
    18.3  (17.9-18.7)   _9_, Valparaíso, Zacatecas.
    18.1  (18.1-18.2)   _4_, Ciudad del Maíz, San Luis Potosí.
    18.6  (18.3-18.9)   _8_, Tepic, Nayarit.
    18.0  (17.7-18.4)  _18_, 4 mi. N, 5 mi. W León, Guanajuato.
    18.1  (17.5-18.9)  _28_, 6 mi. E Querétaro, Querétaro.
    17.7  (17.1-18.1)  _17_, 1 mi. SSE Ameca, Jalisco.
    17.3  (16.8-17.9)  _10_, 2 mi. SSE Autlán, Jalisco.
    18.0  (17.5-18.6)  _10_, 1 mi. S, 11 mi. W Zamora, Michoacán.
    17.6  (17.4-18.2)   _8_, Colima, Colima.


    _Baiomys musculus_

    20.2  (19.9-20.3)  _6_, vic. (see p. 622) Ameca, Jalisco.
    20.2  (19.9-20.3)  _6_, 2 mi. SSE Autlán, Jalisco.
    19.6  (19.2-20.1)  _6_, Jalapa, Veracruz.
    20.3  (19.7-20.9)  _9_, Colima, Colima.
    19.5  (19.0-20.0) _10_, Cerro Gordo, Veracruz.
    19.8  (19.4-20.3)  _6_, 6 mi. S Izucár de Matemores, Puebla.
    20.0  (18.8-20.5)  _7_, Teotitlán, Oaxaca.
    20.1  (19.7-20.7)  _7_, 1 km. NW Chapa, Guerrero.
    19.9  (19.4-20.4)  _8_, 5 mi. ESE Tecpán, Guerrero.
    19.5  (19.1-20.1) _22_, 3 mi. ESE Oaxaca, Oaxaca.
    19.5  (19.1-19.9) _11_, Valley of Comitán, Chiapas.
    18.9  (18.2-20.1) _17_, Tehuantepec, Oaxaca.
    18.9  (18.4-19.7) _15_, 6 mi. NW Tonalá, Chiapas.
    19.1  (18.8-20.4) _10_, 1 mi. S Rabinal, Guatemala.
    19.7  (18.8-20.4) _10_, Lake Amatitlán, Guatemala.
    19.2  (18.4-19.8) _26_, vic. (see p. 625) San Salvador, El Salvador.
    19.3  (18.9-19.9) _24_, 8 mi. S Condega, Estelí, Nicaragua.]




CONCLUSIONS


1. Two Recent species, each polytypic with eight subspecies, and five
fossil species are recognized.

2. The phyletic trends in the genus _Baiomys_ have been from an
ancestral stock that possessed relatively brachydont teeth having raised
cingular ridges and orthodont to proödont incisors, to species having
hypsodont teeth with reduced cingular ridges and retrodont incisors.

3. Reduction of cingular ridges in pygmy mice is associated with an
existence in open grassland (more xeric than mesic), whereas, the
presence of cingular ridges is associated with an existence in a
savannah habitat (more mesic than xeric).

4. Shifts of geographical range of populations of pygmy mice at and near
the periphery of their geographic range may account for the
differentiation of the extinct species.

5. The two living species, _B. musculus_ and _B. taylori_, are seemingly
derived from a common ancestor that in morphological structure was
intermediate between _B. minimus_ and _B. musculus_.

6. The living species of pygmy mice resulted from a geographic
separation, perhaps occurring in the Iowan glacial period (See De Terra,
1949:51) in the transverse volcanic zone of central México.

7. The two species are now sympatric in west central México, where
morphological characters (size and shape of body and length of skull)
differ most. Where the two species are allopatric, these same
morphological characters differ least.

8. This is a documented instance of character displacement in mammals.

9. On the basis of internal morphological characters studied (auditory
ossicles, hyoid apparatus, and baculum), _Baiomys_ seems to be more
closely related to a South American hesperomine, perhaps _Calomys_, than
to any North American cricetine.

10. Pygmy mice were more widely distributed in the past than they are at
present. Part of the ancestral stock of the pygmy mice may have
emigrated from North America into South America in a brief period in the
Pliocene; if so, it is easy to understand why certain South American
hesperomines resemble _Baiomys_.

11. The combination of morphological and behavioral characters in the
living pygmy mice warrants generic status for them. If _Baiomys_ were
treated as a subgenus of the genus _Peromyscus_, there would be adequate
justification for including in the genus _Peromyscus_ a number of other
genera, some of them occurring in South America. Such lumping of genera
would reduce our understanding of the natural relationships among this
group of cricetine rodents.




LITERATURE CITED


  ALLEN, J. A.

  1903.  List of mammals collected by Mr. J. H. Batty in New Mexico and
         Durango, with descriptions of new species and subspecies. Bull.
         Amer. Mus. Nat. Hist., 19:587-612, November 12.


  ALLEN, J. A., and CHAPMAN, F. M.

  1897.  On a collection of mammals from Jalapa and Las Vigas, state of
         Veracruz. Bull. Amer. Mus. Nat. Hist., 9:197-208, June 16.


  AXELROD, D. I.

  1950.  Evolution of the desert vegetation in western North America.
         Carnegie Inst. Washington (Contrib. Paleo.), Publ. 590(6):215-306,
         4 figs., 3 pls., 1 table, December 27.


  BAILEY, V.

  1905.  Biological survey of Texas. N. Amer. Fauna, 25:1-222, 16 pls.,
         24 figs., October 24.


  BAKER, R. H.

  1951.  Mammals from Tamaulipas México. Univ. Kansas Publ., Mus. Nat.
         Hist., 5:207-218, December 15.


  BLAIR, W. F.

  1941.  Observations on the life history of _Baiomys taylori subater_.
         Jour. Mamm., 22:378-383, 1 fig., November 14.

  1942.  Systematic relationships of _Peromyscus_ and several related
         genera as shown by the baculum. Jour. Mamm., 23:196-204, 2 figs.,
         1 table, May 14.

  1952.  Mammals of the Tamaulipan Biotic Province in Texas. Texas
         Jour. Sci., 4:230-250, 1 fig., 2 tables, June 30.

  1953.  Population dynamics of rodents and other small mammals. Advances
         in Genetics, 5:1-41, 1 table.


  BLAIR, W. F., and BLOSSOM, P. M.

  1948.  Variation in the pygmy mouse (_Baiomys taylori_) from Texas and
         Arizona. Contrib. Lab. Vert. Biol., Univ. Michigan, 40:1-7, 3
         tables, March.


  BLOSSOM, P. M., and BURT, W. H.

  1942.  A new race of pygmy mouse (_Baiomys_) from Arizona. Occas.
         Papers, Univ. Michigan, 465:1-4, October 8.


  BOOTH, E. S.

  1957.  Mammals collected in Mexico from 1951 to 1956 by the Walla
         Walla College Museum of Natural History. Walla Walla College
         Publs., Dept. Biol. Sci. and Biol. Station, 20:1-19, 4 unnumbered
         figures, July 10.


  BROWN, W. L.

  1958.  Some zoological concepts applied to problems in evolution of the
         hominid lineage. Amer. Scientist, 46:151-158, 1 fig., June.


  BROWN, W. L., JR., and WILSON, E. O.

  1956.  Character displacement. Soc. Syst. Zool., 5:49-64, 6 figs., June.


  BURT, W. H.

  1936.  A study of the baculum in the genera _Perognathus_ and
         _Dipodomys_. Jour. Mamm., 17:145-156, 6 figs., 2 tables, May 14.

  1938.  Faunal relationships and geographic distribution of mammals in
         Sonora, México. Miscl. Publ. Mus. Zool., Univ. Michigan, 39:1-77,
         2 tables, 26 maps, February 15.


  CLARK, F. H.

  1941.  Correlation and body proportions in mature mice of the genus
         _Peromyscus_. Jour. Genetics, 26:283-300, 8 tables, May.


  COLLINS, H. H.

  1918.  Studies of normal moult and of artificially induced regeneration
         of pelage in _Peromyscus_. Jour. Exper. Zool., 27:73-95, 3 figs.,
         2 pls., October.

  1924.  Studies of the pelage phases and of the nature of color variations
         in mice of the genus _Peromyscus_. Jour. Exper. Zool., 38:45-107,
         57 figs.


  DALQUEST, W. W.

  1953.  Mammals of the Mexican state of San Luis Potosí. Louisiana
         State Univ. Studies, Biol. Ser., 1:1-229, 1 fig., December 28.


  DAVIS, W. B.

  1944.  Notes on Mexican mammals. Jour. Mamm., 25:370-403, 1 fig.,
         3 tables, November 12.


  DAVIS, W. B., and RUSSELL, J. R., JR.

  1954.  Mammals of the Mexican state of Morelos. Jour. Mamm., 35:63-80,
         February 10.


  DETERRA, H., ROMERO, J., and STEWARD, T. D.

  1949.  Tepexpan Man. Viking Fund Publ. in Anthropology, 11:1-160, 22
         figs., 37 pls., 10 tables.


  DICE, L. R.

  1943.  The biotic provinces of North America. Univ. Michigan Press,
         Ann Arbor, viii + 78 pp., 1 map.

  DICE, L. R., and LERAAS, H. J.

  1936.  A graphic method for comparing several sets of measurements.
         Contrib. Lab. Vert. Genetics, Univ. Michigan, 3:1-3, 1 fig., July.


  DOBZHANSKY, T.

  1951.  Genetics and the origin of species. Columbia Univ. Press,
         x + 364 pp., 23 figs., 15 tables.


  DUELLMAN, W. E.

  1958.  A monographic study of the colubrid snake genus _Leptodeira_.
         Bull. Amer. Mus. Nat. Hist., 114(1):1-152, 25 figs., 31 pls.,
         25 maps, 30 tables, February 24.


  DUNN, E. R.

  1940.  Some aspects of herpetology in lower Central America. Trans.
         New York Acad. Sci., 2:156-158, April.


  ELLERMAN, J. R.

  1941.  The families and genera of living rodents with a list of named
         forms (1758-1936). British Museum (Nat. Hist.), London, 2:
         xii + 690, 50 figs., March 21.


  FELTEN, H.

  1958.  Nagetiere (Mammalia, Rodentia) aus El Salvador. Senckenbergiana
         Biologica, 39:133-144, August 30.


  FINDLEY, J. S.

  1955.  Speciation of the wandering shrew. Univ. Kansas Publ., Mus.
         Nat. Hist., 9:1-68, 18 figs., 1 table, December 10.


  GAZIN, C. LEWIS

  1942.  The late Cenozoic vertebrate faunas from the San Pedro Valley,
         Ariz. Proc. U. S. Nat. Mus., 92(3155):475-518.


  GIDLEY, J. W.

  1922.  Preliminary report on fossil vertebrates of the San Pedro Valley,
         Arizona, with descriptions of new species of Rodentia and
         Lagomorpha. U. S. Geol. Surv. Prof. Paper, 131:119-131, 2 pls.,
         March 15.


  GOLDMAN, E. A.

  1951.  Biological investigations in México. Smiths. Miscl. Coll., 115:
         xiii + 476, frontispiece, 71 pls., 1 map, July 31.


  GOLDMAN, E. A. and MOORE, R. T.

  1945.  The biotic provinces of México. Jour. Mamm., 26:347-360, 1 fig.,
         November 14.


  GOODWIN, G. G.

  1934.  Mammals collected by A. W. Anthony in Guatemala, 1924-1928.
         Bull. Amer. Mus. Nat. Hist., 68:1-60, pls. 1-5, December 12.

  1942.  Mammals of Honduras. Bull. Amer. Mus. Nat. Hist., 79:107-195,
         May 29.

  1959.  A new pygmy mouse of the genus _Baiomys_ from Oaxaca, Mexico.
         Amer. Mus. Novit., 1929:1-2, March 5.


  HALL, E. R.

  1959.  Geographic distribution of contemporary organisms, pp. 371-373,
         _in_ Zoogeography. Publ., Amer. Assoc. Adv. Sci., 55:x + 509 pp.
         January 19.


  HALL, E. R., and KELSON, K. R.

  1959.  The mammals of North America. 2 Vols., xxx + 1083 pp. (79 pp.
         index), 553 figs., 500 maps, March 31, 1959.


  HALL, E. R., and VILLA-R., B.

  1949.  An annotated check list of the Mammals of Michoacán, México.
         Univ. Kansas Publ., Mus. Nat. Hist., 1:431-472, pls. 4-5, 1 fig.,
         December 27.


  HERSHKOVITZ, P.

  1944.  A systematic review of the neotropical water rats of the genus
         _Nectomys_ (Cricetinae). Miscl. Publ. Mus. Zool., Univ. Michigan,
         58:1-101, 4 pls., 5 figs., 2 maps, 19 tables, January 4.

  1955.  South American marsh rats Genus _Holochilus_ with a summary of
         sigmodont rodents. Fieldiana-Zool., Chicago Nat. Hist. Mus.,
         37:639-673, 6 figs., 29 pls., 5 tables, June 19.

  1958.  A geographical classification of neotropical mammals.
         Fieldiana-Zool., Chicago Nat. Hist. Mus., 36:583-620, 2 figs.,
         13 tables, July 11.


  HIBBARD, C. W.

  1941.  Paleoecology and correlation of the Rexroad Fauna from the upper
         Pliocene of southwestern Kansas, as indicated by the mammals.
         Univ. Kansas Sci. Bull., 27:79-104, 1 fig., December 15.

  1952.  A contribution to the Rexroad Fauna. Trans. Kansas Acad. Sci.,
         55:196-208, 2 figs., June 18.

  1953.  The saw rock canyon fauna and its stratigraphic significance.
         Papers, Michigan Acad. Sci., Arts and Letters, 38:387-411,
         5 figs., April 27.

  1958.  Summary of North American Pleistocene mammalian local faunas.
         Papers, Michigan Acad. Sci., Arts and Letters, 43:3-32, 1 table.


  HOFFMEISTER, D. F.

  1951.  A taxonomic and evolutionary study of the pinon mouse, _Peromyscus
         truei_. Ill. Biol. Monogr., 21:x + 104, 5 pls., 24 figs.,
         7 tables, November 12.

  1956.  Mammals of the Graham (Pinaleno) Mountains, Arizona. Amer.
         Midland Nat., 55:257-288, 7 figs., 1 table, April.


  HOOPER, E. T.

  1947.  Notes on Mexican mammals. Jour. Mamm., 28:40-57, February 15.

  1949.  Faunal relationships of recent North American rodents. Miscl.
         Publ. Mus. Zool., Univ. Michigan, 72:1-28, 5 tables, May 20.

  1952a. Notes on the pygmy mouse (_Baiomys_), with description of a
         new subspecies from México. Jour. Mamm., 33:90-97, 3 figs.,
         February 18.

  1952b. A systematic review of the harvest mice (genus _Reithrodontomys_)
         of Latin America. Miscl. Publ. Mus. Zool., Univ. Michigan,
         77:1-255, 9 pls., 24 figs., 12 maps, 7 tables, January 16.

  1953.  Notes on the mammals of Tamaulipas, México. Occas. Papers
         Mus. Zool., Univ. Michigan, 544:1-12, March 25.

  1955a. Extra teeth in the pygmy mouse, _Baiomys musculus_. Jour. Mamm.,
         36:298-299, May 26.

  1955b. Notes on Mammals of western México. Occas. Papers Mus. Zool.,
         Univ. Michigan, 565:1-26, November 9.

  1957.  Dental patterns in mice of the Genus _Peromyscus_. Miscl. Publ.
         Mus. Zool., Univ. Michigan, 99:1-59, 24 figs., 3 tables, March 28.

  1958.  The male phallus in mice of the genus _Peromyscus_. Miscl. Publ.
         Mus. Zool., Univ. Michigan, 105:1-24, 1 fig., 24 pls., 1 table,
         December 29.


  HUNSAKER, D., RAUN, G. G., and SWINDELLS, J. E.

  1959.  Range expansion of _Baiomys taylori_ in Texas. Jour. Mamm.,
         40:477-478, August 20.


  KOOPMAN, K. F.

  1950.  Natural selection for reproductive isolation between _Drosophila
         pseudoobscura_ and _Drosophila persimilis_. Evolution, 4:135-148,
         3 figs., 7 tables, June.


  LACK, D.

  1944.  Ecological aspects of species formation in passerine birds. Ibis,
         86:260-286, July.


  LAYNE, JAMES N.

  1959.  Growth and development of the eastern harvest mouse,
         _Reithrodontomys humulis_. Bull. Florida State Mus., 4:61-82,
         5 figs., April 27.


  LEOPOLD, A. S.

  1950.  Vegetation zones of México. Ecol., 31:507-518, 1 fig., 1 table,
         October.


  LOWERY, G. H., and DALQUEST, W. W.

  1951.  Birds from the state of Veracruz, México. Univ. Kansas Publ.,
         Mus. Nat. Hist., 3:531-649, 7 figs., 2 tables, October 10.


  LUKENS, P. W., JR.

  1955.  The mammals of the Chilpancingo area of the Mexican state of
         Guerrero. Unpublished Master's dissertation, Texas Agricultural
         and Mechanical College of Texas. 209 pp.


  MAYR, E.

  1949.  Speciation and selection. Proc. Amer. Phil. Soc., 93:514-519,
         December.


  MEARNS, E. A.

  1907.  Mammals of the Mexican boundary of the United States ... Pt.
         1, Families Didelphidae to Muridae. Bull. U. S. Nat. Mus.,
         56:xv + 530, 13 pls., 126 figs., numerous tables, April 13.


  MERRIAM, C. HART

  1892.  Descriptions of new mammals collected by E. W. Nelson in the
         states of Colima and Jalisco, México. Proc. Biol. Soc. Washington,
         7:164-174, September 29.


  MOORE, R. T.

  1945.  The transverse volcanic biotic province of central México and its
         relationship to adjacent provinces. Trans. San Diego Soc. Nat.
         Hist., 10:217-236, 1 map, 4 tables, August 31.


  OSGOOD, W. H.

  1909.  Revision of the mice of the American Genus _Peromyscus_. N. Amer.
         Fauna, 28:1-285, 8 pls., 12 figs., several tables, April 17.


  PACKARD, R. L.

  1958a. New subspecies of the rodent _Baiomys_ from Central America.
         Univ. Kansas Publ., Mus. Nat. Hist., 9:397-404, 2 tables,
         December 19.

  1958b. The taxonomic status of _Peromyscus allex_ Osgood. Proc. Biol.
         Soc. Washington, 71:17-20, April 11.


  RIDGWAY, R.

  1912.  Color standards and color nomenclature. Published by the author,
         Washington, D. C., iii + 43 pp., 53 pls.


  RINKER, G. C.

  1954.  The comparative myology of the mammalian genera _Sigmodon_,
         _Oryzomys_, _Neotoma_, and _Peromyscus_ (Cricetinae), with remarks
         on their intergeneric relationships. Miscl. Publ. Mus. Zool.,
         Univ. Michigan, 83:1-124, 18 figs., 2 tables, June 4.


  RUSSELL, R. J., JR.

  1952.  A new subspecies of pygmy mouse, _Baiomys musculus_, from
         Morelos, México. Proc. Biol. Soc. Washington, 65:21-22,
         January 29.


  SEARS, P. B.

  1955.  Palynology in southern North America, Part 4: Pleistocene Climate
         in México. Bull. Geol. Soc. America, 66:521-530, 6 figs., 1 pl.,
         1 table, May.


  SIMPSON, G. G.

  1945.  The principles of classification and a classification of mammals.
         Bull. Amer. Mus. Nat. Hist., 85:xvi + 350, October 5.

  1950.  History of the fauna of Latin America.  Amer. Sci., 38(3):361-389,
         10 figs.


  SMITH, H. M.

  1949.  Herpetogeny in México and Guatemala. Ann. Association Amer.
         Geogr., 39:219-238, 1 fig., 1 table, September.


  SPRAGUE, J. M.

  1941.  A study of the hyoid apparatus of the cricetinae. Jour. Mamm.,
         22:296-310, 5 figs., August 14.


  STICKEL, L. F., and STICKEL, W. H.

  1949.  A _Sigmodon_ and _Baiomys_ population in ungrazed and unburned
         Texas prairie. Jour. Mamm., 30:141-150, 3 tables, May 23.


  STUART, L. C.

  1954.  A description of a subhumid corridor across northern central
         America, with comments on its herpetofaunal indicators. Contrib.
         Lab. Vert. Biol., Univ. Michigan, 65:1-26, 6 maps, 6 pls., March.


  TAMAYO, JORGE L.

  1949.  Atlas Geografico general de México, con cartas fisicas,
         biologicas, demograficas, sociales, economicas, y cartogramas,
         Mexico, 24 maps, December 12.


  THOMAS, O.

  1888.  On the small mammals of Duval County, Texas. Proc. Zool.
         Soc. London, pp. 443-450.


  TRUE, F. W.

  1894.  On the relationships of Taylor's Mouse, _Sitomys taylori_. Proc.
         U. S. Nat. Mus., 16:757-758, February 7.


  TWENTE, J. H., and BAKER, R. H.

  1951.  New records of mammals from Jalisco, México, from barn owl
         pellets. Jour. Mamm., 32:120-121, 1 table, February 15.


  VAN GELDER, R. G.

  1959.  A taxonomic revision of the spotted skunks (Genus _Spilogale_).
         Bull. Amer. Mus. Nat. Hist., 117(5):229-392, 47 figs., 32 tables,
         June 15.


  WHITE, J. A.

  1951.  A practical method for mounting the bacula of small mammals.
         Jour. Mamm., 32:125, February 15.

  1953.  The baculum in the chipmunks of western North America. Univ.
         Kansas Publ., Mus. Nat. Hist., 5:611-631, 19 figs., December 1.


  WILSON, R. W.

  1937.  Pliocene rodents of western North America. Carnegie Inst.
         Washington, Publ. 487:21-73, 2 figs., July 23.


  WOOD, A. E., and WILSON, R. W.

  1936.  A suggested nomenclature for the cusps of the cheek teeth of
         rodents. Jour. Paleon., 10:388-391, 2 figs.


_Transmitted March 4, 1960._


[]
28-3030




UNIVERSITY OF KANSAS PUBLICATIONS

MUSEUM OF NATURAL HISTORY


Institutional libraries interested in publications exchange may obtain
this series by addressing the Exchange Librarian, University of Kansas
Library, Lawrence, Kansas. Copies for individuals, persons working in a
particular field of study, may be obtained by addressing instead the
Museum of Natural History, University of Kansas, Lawrence, Kansas. There
is no provision for sale of this series by the University Library, which
meets institutional requests, or by the Museum of Natural History, which
meets the requests of individuals. However, when individuals request
copies from the Museum, 25 cents should be included, for each separate
number that is 100 pages or more in length, for the purpose of defraying
the costs of wrapping and mailing.

    * An asterisk designates those numbers of which the Museum's supply
      (not the Library's supply) is exhausted. Numbers published to date,
      in this series, are as follows:

   Vol.  1. Nos. 1-26 and index. Pp. 1-638, 1946-1950.

  *Vol.  2. (Complete) Mammals of Washington. By Walter W. Dalquest.
                Pp. 1-444, 140 figures in text. April 9, 1948.

   Vol.  3. *1. The avifauna of Micronesia, its origin, evolution, and
                distribution. By Rollin H. Baker, Pp. 1-359, 16 figures in
                text. June 12, 1951.

            *2. A quantitative study of the nocturnal migration of birds.
                By George H. Lowery, Jr. Pp. 361-472, 47 figures in text.
                June 29, 1951.

             3. Phylogeny of the waxwings and allied birds. By M. Dale
                Arvey. Pp. 473-530, 49 figures in text, 13 tables.
                October 10, 1951.

             4. Birds from the state of Veracruz, Mexico. By George H.
                Lowery, Jr., and Walter W. Dalquest. Pp. 531-649,
                7 figures in text, 2 tables. October 10, 1951.

            Index. Pp. 651-681.

  *Vol.  4. (Complete) American weasels. By E. Raymond Hall. Pp. 1-466,
                41 plates, 31 figures in text. December 27, 1951.

   Vol.  5. Nos. 1-37 and index. Pp. 1-676,  1951-1953.

  *Vol.  6. (Complete) Mammals of Utah, _taxonomy and distribution_.
                By Stephen D. Durrant. Pp. 1-549, 91 figures in text,
                30 tables. August 10, 1952.

   Vol.  7. *1. Mammals of Kansas. By E. Lendell Cockrum. Pp. 1-303.
                73 figures in text, 37 tables. August 25, 1952.

             2. Ecology of the opossum on a natural area in northeastern
                Kansas. By Henry S. Fitch and Lewis L. Sandidge.
                Pp. 305-338, 5 figures in text. August 24, 1953.

             3. The silky pocket mice (Perognathus flavus) of Mexico.
                By Rollin H. Baker. Pp. 339-347, 1 figure in text.
                February 15, 1954.

             4. North American jumping mice (Genus Zapus). By Philip H.
                Krutzch. Pp. 349-472, 47 figures in text, 4 tables.
                April 21, 1954.

             5. Mammals from Southeastern Alaska. By Rollin H. Baker and
                James S. Findley. Pp. 473-477. April 21, 1954.

             6. Distribution of Some Nebraskan Mammals. By J. Knox Jones,
                Jr. Pp. 479-487. April 21, 1954.

             7. Subspeciation in the montane meadow mouse. Microtus
                montanus, in Wyoming and Colorado. By Sydney Anderson.
                Pp. 489-506, 2 figures in text. July 23, 1954.

             8. A new subspecies of bat (Myotis velifer) from southeastern
                California and Arizona. By Terry A. Vaughan. Pp. 507-512.
                July 23, 1954.

             9. Mammals of the San Gabriel mountains of California.
                By Terry A. Vaughan. Pp. 513-582. 1 figure in text,
                12 tables. November 15, 1954.

            10. A new bat (Genus Pipistrellus) from northeastern Mexico.
                By Rollin H. Baker. Pp. 583-586. November 15, 1954.

            11. A new subspecies of pocket mouse from Kansas. By E. Raymond
                Hall. Pp. 587-590. November 15, 1954.

            12. Geographic variation in the pocket gopher, Cratogeomys
                castanops, in Coahuila, Mexico. By Robert J. Russell and
                Rollin H. Baker. Pp. 591-608. March 15, 1955.

            13. A new cottontail (Sylvilagus floridanus) from northeastern
                Mexico. By Rollin H. Baker. Pp. 609-612. April 8, 1955.

            14. Taxonomy and distribution of some American shrews.
                By James S. Findley. Pp. 613-618. June 10, 1955.

            15. The pigmy woodrat, Neotoma goldmani, its distribution and
                systematic position. By Dennis G. Rainey and Rollin H.
                Baker. Pp. 619-624, 2 figures in text. June 10, 1955.

            Index. Pp. 625-651.

   Vol.  8.  1. Life history and ecology of the five-lined skink, Eumeces
                fasciatus. By Henry S. Fitch. Pp. 1-156, 26 figures in
                text. September 1, 1954.

             2. Myology end serology of the Avian Family Fringillidae,
                a taxonomic study. By William B. Stallcup. Pp. 157-211,
                23 figures in text, 4 tables. November 15, 1954.

             3. An ecological study of the collared lizard (Crotaphytus
                collaris). By Henry S. Fitch. Pp. 213-274, 10 figures in
                text. February 10, 1956.

             4. A field study of the Kansas ant-eating frog, Gastrophryne
                olivacea. By Henry S. Fitch. Pp. 275-306, 9 figures in
                text. February 10, 1956.

             5. Check-list of the birds of Kansas. By Harrison E.
                Tordoff. Pp. 307-359, 1 figure in text. March 10, 1956.

             6. A population study of the prairie vole (Microtus
                ochrogaster) in northeastern Kansas. By Edwin P. Martin.
                Pp. 361-416, 19 figures in text.  April 2, 1956.

             7. Temperature responses in free-living amphibians and
                reptiles of northeastern Kansas. By Henry S. Fitch.
                Pp. 417-476, 10 figures in text, 6 tables. June 1, 1956.

             8. Food of the crow, Corvus brachyrhynchos Brehm, in
                south-central Kansas. By Dwight Platt. Pp. 477-498.
                4 tables. June 8, 1956.

             9. Ecological observations on the woodrat, Neotoma floridana.
                By Henry S. Fitch and Dennis G. Rainey. Pp. 499-533,
                3 figures in text. June 12, 1956.

            10. Eastern woodrat, Neotoma floridana: Life history and
                ecology. By Dennis G. Rainey. Pp. 535-646, 12 plates,
                13 figures in text. August 15, 1956.

            Index. Pp. 647-675.

   Vol.  9.  1. Speciation of the wandering shrew. By James S. Findley.
                Pp. 1-68, 18 figures in text. December 10, 1955.

             2. Additional records and extensions of ranges of mammals from
                Utah. By Stephen D. Durrant, M. Raymond Lee, and Richard M.
                Hansen. Pp. 69-80. December 10, 1955.

             3. A new long-eared myotis (Myotis evotis) from northeastern
                Mexico. By Rollin H. Baker and Howard J. Stains. Pp. 81-84.
                December 10, 1955.

             4. Subspeciation in the meadow mouse, Microtus
                pennsylvanicus, in Wyoming. By Sydney Anderson.
                Pp. 85-104, 2 figures in text. May 10, 1956.

             5. The condylarth genus Ellipsodon. By Robert W. Wilson.
                Pp. 105-116, 6 figures In text. May 19, 1956.

             6. Additional remains of the multituberculate genus
                Eucosmodon. By Robert W. Wilson. Pp. 117-123, 10 figures
                in text. May 19, 1956.

             7. Mammals of Coahuila, Mexico. By Rollin H. Baker.
                Pp. 125-335, 75 figures in text. June 15, 1956.

             8. Comments on the taxonomic status of Apodemus peninsulae,
                with description of a new subspecies from North China.
                By J. Knox Jones, Jr. Pp. 337-346, 1 figure in text,
                1 table. August 15, 1956.

             9. Extensions of known ranges of Mexican bats. By Sydney
                Anderson. Pp. 347-351. August 15, 1956.

            10. A new bat (Genus Leptonycteris) from Coahuila. By Howard J.
                Stains. Pp. 353-356. January 21, 1957.

            11. A new species of pocket gopher (Genus Pappogeomys) from
                Jalisco, Mexico. By Robert J. Russell. Pp. 357-361.
                January 21, 1957.

            12. Geographic variation in the pocket gopher, Thomomys bottae,
                in Colorado. By Phillip M. Youngman. Pp. 363-385, 7 figures
                in text. February 21, 1958.

            13. New bog lemming (genus Synaptomys) from Nebraska.
                By J. Knox Jones, Jr. Pp. 385-388. May 12, 1958.

            14. Pleistocene  bats from San Josecito Cave, Nuevo León,
                México. By J. Knox Jones, Jr. Pp. 389-396.
                December 19, 1958.

            15. New Subspecies of the rodent Baiomys from Central America.
                By Robert L. Packard. Pp. 397-404. December 19, 1958.

            16. Mammals of the Grand Mesa, Colorado. By Sydney Anderson.
                Pp, 405-414, 1 figure in text. May 20, 1959.

            17. Distribution, variation, and relationships of the montane
                vole, Microtus montanus. By Emil K. Urban. Pp. 415-511.
                12 figures in text, 2 tables. August 1, 1959.

            18. Conspecificity of two pocket mice, Perognathus goldmani and
                P. artus. By E. Raymond Hall and Marilyn Bailey Ogilvie.
                Pp. 513-518, 1 map. January 14, 1960.

            19. Records of harvest mice, Reithrodontomys, from Central
                America, with description of a new subspecies from
                Nicaragua. By Sydney Anderson and J. Knox Jones, Jr.
                Pp. 519-529. January 14, 1960.

            20. Small carnivores from San Josecito Cave (Pleistocene),
                Nuevo León, México. By E. Raymond Hall. Pp. 531-538,
                1 figure in text. January 14, 1960.

            21. Pleistocene pocket gophers from San Josecito Cave, Nuevo
                León, México. By Robert J. Russell. Pp. 539-548, 1 figure
                in text. January 14, 1960.

            22. Review of the insectivores of Korea. By J. Knox Jones, Jr.,
                and David H. Johnson. Pp. 549-578. February 23, 1960.

            23. Speciation and evolution of the pygmy mice, genus Baiomys.
                By Robert L. Packard. Pp. 579-670, 4 plates, 12 figures in
                text. June 16, 1960.

            Index will follow.

   Vol. 10.  1. Studies of birds killed in nocturnal migration. By
                Harrison B. Tordoff and Robert M. Mengel. Pp. 1-44,
                6 figures in text, 2 tables. September 12, 1956.

             2. Comparative breeding behavior of Ammospiza caudacuta and
                A. maritime. By Glen E. Woolfenden. Pp. 45-75, 6 plates,
                1 figure. December 20, 1956.

             3. The forest habitat of the University of Kansas Natural
                History Reservation. By Henry S. Fitch and Ronald R.
                McGregor. Pp. 77-127, 2 plates, 7 figures in text,
                4 tables. December 31, 1956.

             4. Aspects of reproduction and development in the prairie vole
                (Microtus ochrogaster). By Henry S. Fitch, Pp. 129-161,
                8 figures in text, 4 tables. December 19, 1957.

             5. Birds found on the Arctic slope of northern Alaska. By
                James W. Bee. Pp. 163-211, pls. 9-10, 1 figure in text.
                March 12, 1958.

             6. The wood rats of Colorado; distribution and ecology.
                By Robert B. Finley, Jr. Pp. 213-552, 34 plates,
                8 figures in text, 35 tables. November 7, 1958.

             7. Home ranges and movements of the eastern cottontail in
                Kansas. By Donald  W. Janes. Pp. 553-572, 4 plates,
                3 figures in text. May 4, 1959.

             8. Natural history of the salamander, Aneides hardyi.
                By Richard F. Johnston and Schad Gerhard. Pp. 573-585.
                October 8, 1959.

             9. A new subspecies of lizard, Cnemidophorus sacki, from
                Michoacán, México. By William E. Duellman. Pp. 587-598,
                2 figures in text. May 2, 1960.

            10. A taxonomic study of the Middle American Snake, Pituophis
                deppei. By William E. Duellman. Pp. 599-612, 1 plate,
                1 figure in text. May 2, 1960.

            Index will follow.

   Vol. 11.  1. The systematic status of the colubrid snake, Leptodeira
                discolor Günther. By William E. Duellman. Pp. 1-9,
                4 figs. July 14, 1958.

             2. Natural history of the six-lined racerunner, Cnemidophorus
                sexlineatus. By Henry S. Fitch. Pp. 11-62, 9 figs.,
                9 tables. September 19, 1958.

             3. Home ranges, territories, and seasonal movements of
                vertebrates of the Natural History Reservation. By Henry
                S. Fitch, Pp. 68-326, 6 plates, 24 figures in text,
                8 tables. December 12, 1958.

             4. A new snake of the genus Geophis from Chihuahua, Mexico.
                By John M. Legler. Pp. 327-334, 2 figures in text.
                January 28, 1959.

             5. A new tortoise, genus Gopherus, from north-central Mexico.
                By John M. Legler. Pp. 335-343. April 24, 1959.

             6. Fishes of Chautauqua, Cowley and Elk counties, Kansas.
                By Artie L. Metcalf. Pp. 345-400, 2 plates, 2 figures in
                text, 10 tables. May 6, 1959.

             7. Fishes of the Big Blue River Basin, Kansas. By W. L.
                Minckley. Pp. 401-442, 2 plates, 4 figures in text,
                5 tables. May 8, 1959.

             8. Birds from Coahuila, México. By Emll K. Urban. Pp. 443-516.
                August 1, 1959.

             9. Description of a new softshell turtle from the southeastern
                United States. By Robert G. Webb. Pp. 517-525, 2 pls.,
                1 figure in text, August 14, 1959.

            10. Natural history of the ornate box turtle, Terrapene ornata
                ornata Agassiz. By John M. Legler. Pp. 527-669, 16 pls.,
                29 figures in text. March 7, 1960.

            Index will follow.

   Vol. 12.  1. Functional morphology of three bats: Eumops, Myotis,
                Macrotus. By Terry A. Vaughan. Pp. 1-153, 4 plates,
                24 figures in text. July 8, 1959.

             2. The ancestry of modern Amphibia: a review of the evidence.
                By Theodore H. Eaton, Jr. Pp. 155-180, 10 figures in text.
                July 10, 1959.

             3. The baculum in microtine rodents. By Sydney Anderson.
                Pp. 181-216, 49 figures in text. February 19, 1960.

             4. A new order of fishlike Amphibia from the Pennsylvanian of
                Kansas. By Theodore H. Eaton, Jr., and Peggy Lou Stewart.
                Pp. 217-240, 12 figures in text. May 2, 1960.

            More numbers will appear In volume 12.




Transcriber's Notes

The text presented is that of the original printed version except for
the revisions below and a few assumed typesetting errors. The subsection
headers under "VARIATION WITH AGE" were converted to italic only to
match the rest. All other section title formatting retained as printed.
The words Miscellaneous and Monograph were abbreviated as Miscl. and
Mongr. respectively. Except for the two variant spellings of one word
(Mexico/México) which were retained, the most prevalent form of accented
words was used.

Both decimal and whole plus fractional part of numbers (i.e., 9-1/2)
were retained as printed. The male and female symbols are represented by
[M] and [F] respectively. Footnotes were all placed at the end of each
species account. The list of KU Publications were compiled after the
article's text.


Typographical Corrections

  Page Correction
  ==== ====================
  591 proödent => proödont
  694 hesperomyines => hesperomines


Text Emphasis

  _Text_ - Italic

  =Text= - Bold