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UNIVERSITY OF KANSAS PUBLICATIONS
MUSEUM OF NATURAL HISTORY

Volume 14, No. 2, pp. 9-27, 1 fig. in text
July 24, 1961



Geographic Variation in the Harvest Mouse,
Reithrodontomys megalotis,
On the Central Great Plains
And in Adjacent Regions

By

J. KNOX JONES, JR. AND B. MURSALO[)G]LU

UNIVERSITY OF KANSAS
LAWRENCE
1961



UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

Editors: E. Raymond Hall, Chairman, Henry S. Fitch,
Robert W. Wilson

Volume 14, No. 2, pp. 9-27, 1 fig. in text
Published July 24, 1961

UNIVERSITY OF KANSAS
Lawrence, Kansas

PRINTED IN
THE STATE PRINTING PLANT
TOPEKA, KANSAS
1961




Geographic Variation in the Harvest Mouse,
Reithrodontomys megalotis,
On the Central Great Plains
And in Adjacent Regions

By

J. KNOX JONES, JR. AND B. MURSALO[)G]LU


The western harvest mouse, _Reithrodontomys megalotis_, inhabits most
parts of the central Great Plains and adjacent regions of tall grass
prairie to the eastward, shows a marked predilection for grassy
habitats, is common in many areas, and is notably less variable
geographically than most other cricetids found in the same region. _R.
megalotis_ occurs (see Hall and Kelson, 1959:586, map 342) from
Minnesota, southwestern Wisconsin, northwestern Illinois, Iowa and
Missouri westward to, but apparently not across, the Rocky Mountains
from southeastern Alberta to Colorado; it is known in Oklahoma only from
the Panhandle, thence southward through the Panhandle and Trans-Pecos
areas of Texas to southern México, westward across the mountains in New
Mexico to the Pacific Coast, and northward to the west of the Rockies to
southern British Columbia.

Hoffmeister and Warnock (1955) studied western harvest mice from
Illinois, Iowa, northeastern Kansas, Minnesota and Wisconsin, concluded
that one subspecific name (_Reithrodontomys megalotis dychei_ J. A.
Allen, 1895, with type locality at Lawrence, Douglas Co., Kansas)
applied to all, and relegated _Reithrodontomys megalotis pectoralis_
Hanson, 1944 (type locality at Westpoint, Columbia Co., Wisconsin) to
synonymy under _dychei_. Our study, based upon an examination of 1350
specimens, concerns the area west of the Missouri River from Kansas and
Nebraska westward to Montana, Wyoming, Colorado and northern New Mexico.
Our objectives were to study variation in _R. megalotis_ in the region
indicated and to decide what subspecific names properly apply to
populations of the species that occur there.

Aside from the name _R. m. dychei_, currently applied to western harvest
mice from a large part of the region here under study, three other
subspecific names need consideration:

    "_Reithrodontomys aztecus_" J. A. Allen, 1893 (type locality, La
    Plata, San Juan Co., New Mexico), currently applied to specimens
    from northern New Mexico and southern Colorado (and adjacent parts
    of Arizona and Utah) east to southwestern Kansas and the Oklahoma
    Panhandle;

    "_Reithrodontomys megalotis caryi_" A. H. Howell, 1935 (type
    locality, Medano Ranch, 15 mi. NE Mosca, Alamosa Co., Colorado),
    proposed for, and currently applied to, harvest mice from the San
    Luis Valley, Colorado, but possibly a synonym of _aztecus_ according
    to Hooper (1952:218); and

    "_Reithrodontomys dychei nebrascensis_" J. A. Allen, 1895 (type
    locality, Kennedy, Cherry Co., Nebraska), proposed for harvest mice
    from western Nebraska and adjacent areas, but regarded as a synonym
    of _dychei_ by A. H. Howell (1914:30-31).

Our comments concerning the taxonomic status of these several names
appear beyond.

    We are grateful to Dr. W. Frank Blair, University of Texas, for the
    loan of a specimen from the Texas Panhandle (TU), and to Dr. Richard
    H. Manville, U.S. Fish and Wildlife Service, for the loan of
    specimens of _R. m. caryi_ from the Biological Surveys Collection
    (USNM). We are grateful also to persons in charge of the following
    collections for allowing one of us (Jones) to examine Nebraskan
    specimens of _R. megalotis_ in their care: University of Michigan
    Museum of Zoology (UMMZ); University of Nebraska State Museum (NSM);
    and U.S. National Museum (USNM). A research grant from the Society
    of the Sigma Xi facilitated travel to the institutions mentioned.
    Specimens not identified as to collection are in the Museum of
    Natural History of The University of Kansas. All measurements are in
    millimeters, and are of adults (as defined by Hooper, 1952:12)
    unless otherwise noted.


Secondary Sexual Variation

Hooper (1952) did not accord separate treatment to males and females in
taxonomic accounts of Latin American harvest mice because (p. 11): "In
no species ... does sexual dimorphism in the measurements, if present at
all, appear to be sufficient to warrant separating the sexes in the
analysis." Hooper did not statistically test the validity of treating
the sexes together in _R. megalotis_. He did test a series of _R.
sumichrasti_ from El Salvador, in which he found no basis for separate
treatment of males and females.

Some authors (Verts, 1960:6, for instance) have recorded females of _R.
megalotis_ as larger than males in external measurements, whereas others
(Dalquest, 1948:325, for instance) have recorded males as the larger. In
order to learn something of secondary sexual variation, and to decide
whether or not to separate the sexes in our study, we compared adult
males and females from the southern part of the Panhandle of Nebraska
(Cheyenne, Keith, Kimball, Morrill and Scotts Bluff counties) in four
external and twelve cranial measurements (see Table 1). The external
measurements are those customarily taken by collectors and were read
from the labels of the specimens; cranial measurements were taken to the
nearest tenth of a millimeter by means of dial calipers, and are those
described by Hooper (1952:9-11). Females from our sample averaged larger
than males in all external and several cranial measurements, but
individual variation greatly exceeded secondary sexual variation in each
of these measurements and in no case was the greater size of females
statistically significant. Therefore, and because we found no
qualitative external or cranial differences between the sexes, males and
females have been considered together in each population studied.

TABLE 1. ANALYSIS OF SECONDARY SEXUAL VARIATION IN ADULT REITHRODONTOMYS
MEGALOTIS FROM THE SOUTHERN PART OF THE NEBRASKA PANHANDLE. FOR EACH
MEASUREMENT, THE NUMBER OF SPECIMENS USED, THE AVERAGE, THE EXTREMES,
AND ONE STANDARD DEVIATION ARE GIVEN.

  CHARACTER  |           Males            |        Females
-------------+--+-----+------------+------+--+-----+----------+-----
Total
length       |27|135.0|(121-149)   |±6.14 |32|141.0|(127-149) |±5.36
-------------+--+-----+------------+------+--+-----+----------+-----
Length of
tail-
vertebrae    |27| 63.9|( 56-74)    |±4.63 |32| 65.2|(58-73)    |±4.06
-------------+--+-----+------------+------+--+-----+-----------+-----
Length
of hind
foot         |27| 17.0|( 16-18)    |±0.60 |32| 17.3|(15-19)    |±0.81
-------------+--+-----+------------+------+--+-----+-----------+-----
Length of
ear from
notch        |27| 12.9|( 12-14)    |±0.55 |32| 13.0|(12-14)    |±0.61
-------------+--+-----+------------+------+--+-----+-----------+-----
Greatest
length of
skull        |27| 21.0|( 20.2-21.8)|±0.43 |28| 21.3|(20.4-22.2)|±0.48
-------------+--+-----+------------+------+--+-----+-----------+-----
Zygomatic
breadth      |25| 10.7|( 10.3-11.0)|±0.21 |28| 10.9|(10.4-11.3)|±0.25
-------------+--+-----+------------+------+--+-----+-----------+-----
Breadth of
braincase    |27| 10.0|(  9.6-10.5)|±0.22 |28| 10.1|(9.8-10.7) |±0.18
-------------+--+-----+------------+------+--+-----+-----------+-----
Depth of
cranium      |26|  7.9|(  7.4-8.4) |±0.20 |28|  7.9|( 7.7-8.3) |±0.15
-------------+--+-----+------------+------+--+-----+-----------+-----
Length of
rostrum      |27|  7.3|(  6.8-7.6) |±0.21 |28|  7.4|( 6.9-8.0) |±0.27
-------------+--+-----+------------+------+--+-----+-----------+-----
Breadth of
rostrum      |27|  3.8|(  3.6-4.1) |±0.11 |28|  3.8|( 3.5-4.0) |±0.12
-------------+--+-----+------------+------+--+-----+-----------+-----
Length of
incisive
foramen      |27|  4.4|(  4.1-4.6) |±0.10 |28|  4.5 ( 4.1-4.9) |±0.19
-------------+--+-----+------------+------+--+-----+-----------+-----
Length of
palate       |26|  3.5|(  3.1-3.8) |±0.18 |28|  3.5 ( 3.2-4.0) |±0.15
-------------+--+-----+------------+------+--+-----+-----------+-----
Alveolar
length of
maxillary
tooth-row    |27|  3.4|(  3.2-3.7) |±0.14 |28|  3.4|( 3.2-3.7) |±0.13
-------------+--+-----+------------+------+--+-----+-----------+-----
Interorbital
breadth      |27|  3.1|(  2.9-3.3) |±0.12 |28|  3.1|( 2.8-3.3) |±0.11
-------------+--+-----+------------+------+--+-----+-----------+-----
Breadth of
zygomatic
plate        |27|  1.9|(  1.8-2.1) |±0.10 |28|  2.0|( 1.9-2.3) |±0.12
-------------+--+-----+------------+------+--+-----+-----------+-----
Breadth of
mesopterygoid
fossa        |26|  0.9|(  0.6-1.1) |±0.12 |28|  0.9|( 0.8-1.2) |±0.12
-------------+--+-----+------------+------+--+-----+-----------+-----


Pelage and Molt

Western harvest mice that attain adulthood acquire at least three
distinct types of pelage in sequence in the course of their development.
The first of these, the juvenal pelage, is short, relatively sparse, and
characteristically grayish brown. The molt (post-juvenal molt) from
juvenal pelage to subadult pelage seemingly occurs at an early age,
perhaps frequently before the young leave the nest, as individuals in
juvenal pelage are few among specimens studied by us. Judging from study
skins alone, the progress of post-juvenal molt in _R. megalotis_ is
similar to that described for _R. humulis_ by Layne (1959:69-71). The
subadult pelage is thicker, longer and brighter than juvenal pelage and
closely resembles the pelage of adults; it differs from adult pelage
dorsally in being somewhat duller and in having less contrast between
back and sides.

The pelage of adults varies depending on season. In summer the
individual hairs are relatively short (5-6 mm. at the middle of the
back) and sparse. The over-all color of the dorsum, sides and flanks is
brownish to dark brownish, and the venter is grayish. In winter the
pelage is dense, long (8-9 mm. at the middle of the back) and lax. The
over-all color dorsally in fresh winter pelage in most specimens is
paler (more buffy) than summer pelage, the sides are markedly buffy, and
the venter is whitish; even the tail is more pilose and more sharply
bicolored than in summer. Adults molt, usually completely but
occasionally only partially, at least twice a year--once in spring (in
May and June in Nebraskan specimens) from winter to summer pelage, and
once in autumn (in October and November in Nebraskan specimens) from
summer to winter pelage. Of the two molts, the one in spring is most
easily discernible because the contrast in color between worn winter
pelage and fresh summer pelage is considerably greater than that between
worn summer pelage and fresh winter pelage, and because the progress of
spring molt is seemingly more regular than that of autumn molt. In
spring, molt proceeds posteriorly in a more or less regular line on both
dorsum and venter; in most specimens it is completed first on the
venter. In autumn, molt is irregular, or at best is coincident over
large parts of the body, and frequently is seen only by searching
through the pelage with a fine probe or dissecting needle. In both
spring and autumn, molt seemingly is delayed in females that are
pregnant or lactating.

In both winter pelage and summer pelage, the upper parts have blackish
or grayish guard hairs and shorter, more numerous cover hairs. All the
cover hairs are gray basally; some have a buffy band terminally and
others have a buffy subterminal band with a terminal black tip. The
generally darker over-all color of upper parts in summer pelage results
(as seen in Nebraskan specimens) from a narrower band of buff on the
cover hairs (only approximately one half the width of the band on hairs
in winter pelage), a darker buffy band (ochraceous buff rather than pale
ochraceous or straw color), and a relative sparseness of the pelage,
which allows the gray basal portion of some hairs to show on the
surface. The more grayish venter of summer-taken specimens results from
much more of the grayish basal portion of the white-tipped hairs showing
through than in the longer, denser pelage of winter.

Wear on the pelage seems in general to produce a paler over-all color of
upper parts, evidently due mostly to abrasion of the terminal black tip
of the cover hairs, but possibly actual fading of the pelage is involved
also. Worn winter pelage is especially notable for its paleness; the
buffy tones are accentuated and the upper parts, especially posteriorly,
may even appear fulvous. The difference in color of upper parts between
specimens in worn winter pelage and fresh summer pelage (or for that
matter specimens in fresh _versus_ worn winter pelage) from the same
locality is greater in our material than the difference between some
specimens in comparable pelages from localities more than 500 miles
apart.

We have seen no specimens taken in winter in which we could discern that
the autumn molt had been incomplete, but three old adult males in summer
pelage indicate that spring molt is not always completed. KU 50154,
obtained on August 14, 1952, 5 mi. N and 2 mi. W Parks, Dundy Co.,
Nebraska, has the entire posterior back and sides still in old winter
pelage and does not appear to have been actively molting; the entire
venter is in summer pelage. KU 50146, obtained on August 22, 1952, 3 mi.
E Chadron, Dawes Co., Nebraska, has small patches or tufts of winter
pelage remaining on the rump and likewise does not appear to have been
actively molting. KU 72085, obtained on October 13, 1956, 4 mi. E
Barada, Richardson Co., Nebraska, is in the process of molting from
summer to winter pelage, but has tufts of old winter pelage on the rump.


Geographic Variation

Geographic variation, both in color of pelage and in external and
cranial dimensions, is less in _R. megalotis_ in the region studied than
in most other cricetine species that occur there. Nevertheless,
meaningful variation is present. The assumption that variation in _R.
megalotis_ paralleled in degree that of other species, _Peromyscus
maniculatus_ for example, led to untenable taxonomic conclusions by some
previous workers.


_Color of Pelage_

Color of pelage is remarkably uniform, considering the geographic extent
of the area involved, over most of the northern part of the central
grasslands. Perhaps this uniformity results partly from the predilection
of the western harvest mouse for grassy habitats, for in most areas on
the Great Plains the species is restricted to riparian communities,
principally along river systems, where soils, cover, and other
conditions approximate those of corresponding habitats farther to the
east to a much greater degree than do conditions in upland habitats.
Differential selective pressure, therefore, theoretically would be less
between eastern and western populations of _R. megalotis_ than in an
upland-inhabiting species. In any event, specimens from western
Nebraska, Wyoming, northern Colorado, and adjacent areas average only
slightly paler dorsally than specimens in corresponding pelages from the
eastern parts of Nebraska and Kansas, and many individuals from the two
areas can be matched almost exactly.

To the southwest, on the other hand, a trend toward paler (pale
brownish, less blackish) upper parts is apparent. Specimens from
southwestern Kansas and adjacent parts of Colorado and Oklahoma average
slightly paler in comparable pelages than specimens from northeastern
Kansas and eastern Nebraska, but most specimens from farther southwest,
in northern New Mexico and southwestern Colorado, are discernibly,
although not markedly, paler than mice from northern and eastern
populations.

A "pectoral spot," fairly common in some populations of _R. megalotis_
east of the Missouri River (see Hoffmeister and Warnock, 1955:162-163),
is present in only a small percentage of the specimens we have studied,
and when present is usually only faintly developed.


_External and Cranial Size_

[Illustration: FIG. 1. Geographic variation in five measurements of
_Reithrodontomys megalotis_ on the central Great Plains. The size of
each sample is given, along with total length, length of tail expressed
as a percentage of the head and body, length of ear, greatest length of
skull, and length of rostrum. The approximate distribution of the
species in the region shown and the approximate boundary between the
subspecies _R. m. aztecus_ and _R. m. dychei_ also are indicated.]

As seen in Figure 1, the tail and especially the ear are longer in mice
from New Mexico and adjacent areas than in specimens from northern
localities. The ear, only slightly variable in size in the northern part
of the region, is markedly longer in the southwest, averaging more than
2 mm. longer in specimens from New Mexico and adjacent southwestern
Colorado than in specimens from Nebraska and eastern Kansas; specimens
in a zone from central Colorado through southwestern Kansas and adjacent
Oklahoma generally have ears of a size between the two extremes. As
concerns the tail we note a slight trend toward increasing length (best
expressed as percentage of length of body) from north to south
throughout the central plains, but in general the trend is more
pronounced southwestwardly. Variation in length of tail and length of
ear, therefore, appear to be in accord with Allen's Rule. Length of body
and length of hind foot seem not to vary significantly in specimens we
have studied.

The skulls of specimens examined differed only slightly, except that the
rostrum is significantly longer and relatively, if not actually,
narrower in specimens from the south and southwest than in mice from the
rest of the region under study. The rostrum is longest (average 7.7 mm.)
in specimens from the vicinity of the type locality of _R. m. aztecus_,
but is relatively long (7.5-7.6 mm.) in populations from as far north as
northeastern Colorado and southwestern Nebraska. An average greater
occipitonasal length (greatest length of skull) in specimens from the
south and southwest results mostly from the longer rostrum.

Recognition of two subspecies of _R. megalotis_ on the central Great
Plains seems justified on the basis of the geographic variation
discussed above. One subspecies, for which the name _R. m. aztecus_ is
applicable, occurs in the southwest and is characterized by the
culmination of trends in the region studied to paler upper parts, longer
tail, longer ear, and longer, relatively narrower rostrum--characters
that appear at least partly independent of each other as concerns
gradation toward the smaller, darker-colored populations to the
northward. The latter, while exhibiting some differences in color
(slightly paler westwardly) and length of tail (shorter northwardly),
stand more or less as a unit in contrast to the mice from the southwest,
and represent, in our judgment, a single subspecies, _R. m. dychei_. The
area of intergradation between the two subspecies is relatively broad,
considering all the characters mentioned, and assignment of some
intergrades is admittedly difficult.


_Reithrodontomys megalotis aztecus_ J. A. Allen

    _Reithrodontomys aztecus_ J. A. Allen, Bull. Amer. Mus. Nat. Hist.,
    5:79, April 28, 1893 (type locality, La Plata, San Juan Co., New
    Mexico).

    _Reithrodontomys megalotis aztecus_, A. H. Howell, N. Amer. Fauna,
    36:30, June 5, 1914.

    _Reithrodontomys megalotis caryi_ A. H. Howell, Jour. Mamm., 16:143,
    May 15, 1935 (type locality, Medano Ranch, 15 mi. NE Mosca, Alamosa
    Co., Colorado).


    _Distribution._--Western and southern Colorado, southeastern Utah,
    northeastern Arizona and northern New Mexico, east to the panhandles
    of Texas and Oklahoma and to southwestern Kansas.

    _External measurements._--Average and extremes of 10 adults (5
    males, 5 females) from San Juan County, New Mexico, and adjacent
    Montezuma County, Colorado, are: total length, 140.1 (126-150);
    length of tail-vertebrae, 67.4 (56-71); length of hind foot, 17.3
    (16-18); length of ear from notch, 15.1 (13-17); tail averaging 92.7
    per cent of length of body. Corresponding measurements of 13 adults
    (7 males, 6 females) from Bernalillo and Guadalupe counties, New
    Mexico, are: 142.1 (129-156); 69.4 (60-75); 17.9 (17-19); 16.3
    (15-18); tail averaging 95.4 per cent of length of body.
    Corresponding measurements of 22 adults (17 males, 5 females) from
    Meade County, southwestern Kansas, are: 147.1 (139-162); 71.3
    (65-77); 17.6 (17-19); 13.8 (13-15); tail averaging 94.1 per cent of
    length of body. For cranial measurements see Table 2.


_Remarks._--For comparisons with _Reithrodontomys megalotis dychei_,
geographically adjacent to the northeast, see account of that
subspecies.

When Howell (1935:143) named _Reithrodontomys megalotis caryi_ from the
San Luis Valley of Colorado he compared it directly only with _R. m.
megalotis_ from southern New Mexico and northern Chihuahua. Few adults
were available to Howell from the San Luis Valley, accounting for the
fact, we think, that the published measurements of _caryi_ average less
than those given for _R. m. aztecus_ by Howell (_op. cit._:144) and
herein. We have examined 16 of the 23 specimens from Medano Ranch and
the single specimen from Del Norte that Howell listed. Unfortunately,
none is fully adult. The specimens from Medano Ranch, collected in late
October and early November, are mostly in fresh winter pelage or molting
from subadult pelage, and closely resemble topotypes of _aztecus_ in
comparable pelages. Comparison of skulls of the specimens from Medano
Ranch with skulls of topotypes and other individuals of _aztecus_ of
approximately equal age indicates that the Coloradan specimens may
average slightly smaller and have somewhat shorter rostra. Externally,
topotypes of _caryi_ have the relatively long tail of _aztecus_ and
approach it in length of ear (measured on dry specimens). To us, they
appear to be intergrades between _aztecus_ and _dychei_, but to bear
closer resemblance to the former, and we tentatively regard _caryi_ as a
synonym of _aztecus_. Benson (1935:140) noted that two adult topotypes
of _caryi_ were "similar to adult topotypes of _aztecus_." Specimens
from southern Colorado east of the San Luis Valley, assigned to
_aztecus_, are intergrades between it and _dychei_, as are two specimens
from El Paso County, to the north, which resemble _aztecus_ in color but
resemble _dychei_ in other characters and are tentatively assigned to
the latter.

Specimens from southwestern Kansas and adjacent Oklahoma, herein
referred to _aztecus_, also are intergrades with _dychei_. Individuals
from Meade County, for example, are intermediate on the average between
typical specimens of the two subspecies in color of upper parts (if
anything, nearer _dychei_), resemble _dychei_ in length of ear, but
resemble _aztecus_ in length of tail and rostral proportions
(consequently also in length of skull). Although a case could be made
for assignment of the specimens from Meade County (and elsewhere in
southwestern Kansas) to _dychei_, they are, everything considered,
nearer _aztecus_, to which subspecies they have been assigned
consistently since first reported from the area by Hill and Hibbard
(1943:24).

Of two specimens examined from 10 mi. S and 1 mi. W Gruver, Hansford
Co., in the Panhandle of Texas, the one adult is clearly assignable to
_aztecus_ as is the specimen from 9 mi. E Stinnett, Hutchinson Co.,
Texas, that was referred to _dychei_ by Blair (1954:249).

_Reithrodontomys megalotis aztecus_ has had a rather unstable taxonomic
history. Allen, who originally named the subspecies (1893:79), regarded
it two years later (1895:125) as a synonym of _R. m. megalotis_, the
subspecies with geographic range to the south and west of that occupied
by _aztecus_. Howell (1914:30) recognized _aztecus_ as valid, but he,
too, questioned its distinctness from _megalotis_ in a later paper
(1935:144). Hooper (1952:218), the most recent reviewer, supported the
validity of _aztecus_ because specimens available to him averaged
"distinctly larger in skull length and size of brain case" than
specimens of _megalotis_. Our comparisons of typical specimens of
_aztecus_ with specimens of _megalotis_ from southern New Mexico and
southwestern Texas confirm Hooper's observations and indicate also that
_aztecus_ has a longer rostrum and slightly longer ear.


    _Specimens examined._--205, as follows:

    COLORADO. _Alamosa County_: Medano Ranch, 15 mi. NE Mosca, 16
    (USNM). _La Plata County_: 1 mi. NW Florida, 6700 ft., 1; Florida,
    6800 ft., 1. _Las Animas County_: 1 mi. S, 7 mi. E Trinidad, 2.
    _Montezuma County_: 1 mi. W Mancos, 5; north end, Mesa Verde Nat'l
    Park, 7000 ft., 3; Far View Ruins, Mesa Verde Nat'l Park, 7700 ft.,
    3; Park Point, Mesa Verde Nat'l Park, 8525 ft., 2; within 3 mi. Rock
    Springs, Mesa Verde Nat'l Park, 7500-8200 ft., 6. _Prowers County_:
    Lamar, 2. _Rio Grande County_: Del Norte, 1 (USNM).

    KANSAS. _Finney County_: 1 mi. S, 2 mi. E Garden City, 4. _Ford
    County_: 1/2 mi. NW Bellefont, 10; 6-1/4 mi. N Fowler, 2. _Grant
    County_: 2 mi. S, 9 mi. W Santanta, 1. _Kearney County_: 3-1/2 mi.
    N, 4 mi. E Lakin, 4. _Meade County_: within 2-1/2 mi. Fowler, 10;
    Meade County State Park, 14 mi. SW Meade, 48; 17 mi. SW Meade, 5.
    _Morton County_: 7-1/2 mi. S Richfield, 4; 8 mi. N Elkhart, 1; 7-1/2
    mi. N, 1-1/2 mi. W Elkhart, 2. _Seward County_: 3 mi. NE Liberal, 1.
    _Stanton County_: 1 mi. N, 6-7-1/2 mi. W Manter, 2; dam of Lake
    Stanton, 1.

    NEW MEXICO. _Bernalillo County_: 6-1/2 mi. E Alameda, 11; 5 mi. W
    Albuquerque, 3. _Catron County_: 1 mi. NE Apache Creek, 4; Apache
    Creek, 2. _Guadalupe County_: 4 mi. SW Santa Rosa, 4700 ft., 10.
    _McKinley County_: Upper Nutria, 7200 ft., 2. _Rio Arriba County_: 4
    mi. N El Rito, 1; 1 mi. SE El Rito, 1. _Sandoval County_: 3 mi. N La
    Cueva Rec. Area, 1. _San Juan County_: 2 mi. N La Plata, 15. _Santa
    Fe County_: 1 mi. W Santa Fe Municipal Airport, 1; La Bajada Grade,
    20 mi. W Santa Fe, 1. _Socorro County_: 2 mi. S San Antonio, 4.

    OKLAHOMA. _Beaver County_: 7 mi. S Turpin, 1. _Texas County_: 3-1/2
    mi. SW Optima, 8.

    TEXAS. _Hansford County_: 10 mi. S, 1 mi. W Gruver, 2. _Hutchinson
    County_: 9 mi. E Stinnett, 1 (TU).


_Reithrodontomys megalotis dychei_ J. A. Allen

    _Reithrodontomys dychei_ J. A. Allen, Bull. Amer. Mus. Nat. Hist.,
    7:120, May 21, 1895 (type locality, Lawrence, Douglas Co., Kansas).

    _Reithrodontomys megalotis dychei_, A. H. Howell, N. Amer. Fauna,
    36:30, June 5, 1914.

    _Reithrodontomys dychei nebrascensis_ J. A. Allen, Bull. Amer. Mus.
    Nat. Hist., 7:122, May 21, 1895 (type locality, Kennedy, Cherry Co.,
    Nebraska).

    _Distribution._--Southwestern Wisconsin, southern Minnesota,
    northwestern Illinois, Iowa, Missouri and northwestern Arkansas,
    west through Kansas (except southwestern part), Nebraska and the
    Dakotas to the foothills of the Rocky Mountains from central
    Colorado to southeastern Alberta.

    _External measurements._--Average and extremes of 17 adults (11
    males, 6 females) from Douglas County, Kansas, are: total length,
    134.2 (115-151); length of tail-vertebrae, 64.2 (59-72); length of
    hind foot, 16.7 (15-18); length of ear from notch, 13.4 (12-15);
    tail averaging 91.7 per cent of length of body. Corresponding
    measurements of 20 adults (14 males, 6 females) from Cherry County,
    Nebraska, are: 135.3 (122-155); 62.9 (56-72); 17.5 (17-18); 13.0
    (12-14); tail averaging 86.9 per cent of length of body. For cranial
    measurements see Tables 1 and 2.


_Remarks._--From _Reithrodontomys megalotis aztecus_, geographically
adjacent to the southwest, _R. m. dychei_ differs as follows: upper
parts averaging darker (especially in summer pelage), owing principally
to more suffusion of blackish middorsally; tail slightly shorter; ears
markedly shorter, rostrum shorter and relatively broader; occipitonasal
length shorter owing to shorter rostrum.

"_Reithrodontomys dychei nebrascensis_," named by Allen (1895:122)
from Kennedy, Nebraska, was distinguished in the original description
from _dychei_ by "slightly larger size, relatively longer ears, and
more strongly fulvous coloration." Allen applied the name _nebrascensis_
to harvest mice from Montana south to central Colorado and western
Nebraska. Howell (1914:30-31) placed _nebrascensis_ in synonymy under
_dychei_ because he found specimens from Kennedy to be "indistinguishable
from specimens of typical _dychei_ in comparable pelage." We concur
with Howell. Topotypes of _nebrascensis_ that we have examined average
only slightly paler than topotypes of _dychei_ in the same pelage (some
specimens from each series can be matched almost exactly), and do not
differ significantly in any external or cranial measurements. The
"fulvous" upper parts of the series from Kennedy (all taken in late
April) that was available to Allen resulted from worn winter pelage. We
think that Allen was led astray also by his erroneous assumption that
geographic variation in color of _R. megalotis_ on the Great Plains
paralleled that found in _Peromyscus maniculatus_. Actually, _R.
megalotis_ varies in color much less geographically in the region
concerned than does _P. maniculatus_.

Specimens from the northwestern part of the range of _dychei_ (Wyoming,
Montana and western South Dakota), like those from western Nebraska,
average slightly paler dorsally than topotypes and other specimens from
eastern Kansas and Nebraska (a few approach _aztecus_ in this regard),
but do not otherwise differ. Most specimens from northern Colorado,
southwestern Nebraska (Hitchcock and Dundy counties) and western Kansas
average slightly paler than typical specimens and have longer rostra,
approaching _aztecus_ in these particulars, but have the shorter ears
and shorter tail of _dychei_. In general, these intergrades resemble
_dychei_ to a greater degree than _aztecus_ and are accordingly assigned
to the former. One exception is a series from Muir Springs, 2 mi. N and
2-1/2 mi. W Ft. Morgan, Colorado. Specimens in this series approach
typical _dychei_ in color, but resemble _aztecus_ in having long ears
and long rostra (average 15.3 and 7.5, respectively, in 13 adults). The
specimens from Muir Springs resemble _aztecus_ to a greater degree than
_dychei_, but are assigned to the latter because specimens from farther
west and farther south in Colorado are assignable to _dychei_. Howell
(1914:31) earlier noted that specimens from northern and central
Colorado were intergrades between the two subspecies.

The geographic range occupied by _R. m. dychei_ (from east of the
Mississippi River in Illinois and Wisconsin to the foothills of the
Rockies) is large (although not so large as that currently ascribed to
_R. m. megalotis_, which ranges from southern British Columbia to
central México). Most other small rodents that occur in the same
geographic area occupied by _dychei_ are represented there by at least
two subspecies, a dark one in the east and a pale one in the west.
Eastern populations of _dychei_ have, it is true, somewhat darker upper
parts than mice from western localities, but the differences are slight;
also, judging from the literature, the "pectoral spot" is more common in
eastern mice.

It should be noted that _R. m. dychei_ probably has extended its range
both eastward and westward in the last century as a result of
agricultural practices--clearing of land in the east and irrigation in
the west.


    _Specimens examined._--1145, as follows:

    COLORADO. _Adams County_: South Platte River, 5 mi. N Denver, 1; 3
    mi. S, 1 mi. W Simpson, 1. _El Paso County_: 5 mi. E Payton, 1; 4
    mi. S maingate of Camp Carson, 1. _Larimer County_: 3 mi. N
    Loveland, 1; 9-1/4 mi. W, 1/2 mi. N Loveland, 5600 ft., 1; 16 mi. W
    Loveland, 6840 ft., 1; 3-1/2-4-1/2 mi. W Loveland, 5030 ft., 7; 6
    mi. W, 1/2 mi. S Loveland, 5200 ft., 14; 7 mi. W, 2-1/2 mi. S
    Loveland, 5370 ft., 1. _Morgan County_: Muir Springs, 2 mi. N, 2-1/2
    mi. W Ft. Morgan, 21. _Washington County_: Cope, 6. _Yuma County_: 1
    mi. W to 1 mi. E Laird, 6.

    KANSAS. _Atchison County_: 1-1/2 mi. S Muscotah, 10; 4-1/2 mi. S
    Muscotah, 2. _Barton County_: 3 mi. N, 2 mi. W Hoisington, 3. _Brown
    County_: 1 mi. E Reserve, 2; 5 mi. S Hiawatha, 4. _Cheyenne County_:
    23 mi. NW St. Francis, 1; 1 mi. W St. Francis, 12; 8 mi. S, 1-1/2
    mi. W St. Francis, 1. _Decatur County_: 1 mi. N, 2 mi. E Oberlin, 4;
    5 mi. S, 8 mi. W Oberlin, 1. _Doniphan County_: Geary, 2. _Douglas
    County_: 5 mi. N, 1/2 mi. E Lawrence, 1; 1 mi. NW Midland, 1; 4-1/2
    mi. N Lawrence, 2; 4 mi. N, 1-3/4 mi. E Lawrence (sec. 8, T. 12 S,
    R. 20 E), 10; 1/2 mi. NW Lecompton, 1; 2-1/2 mi. N, 1 mi. W
    Lawrence, 2; 2 mi. N Lawrence, 2; U.P. Railroad tracks, N of
    Lawrence, 1; 9-1/5 mi. W Lawrence, 1; 5 mi. W Lawrence, 1; 2 mi. W
    Lawrence, 4; 1 mi. W Lawrence, 4; Fort Lake, Lawrence, 1; Lawrence,
    24; 1 mi. SW Lawrence, 2; 1 mi. S, 1-1/2 mi. W Lawrence, 2; 1-3/4.
    mi. S, 3-1/2 mi. E Lawrence, 1; 2 mi. SW Lawrence, 2; 7-7-1/2 mi. SW
    Lawrence, 4; Rock Creek, 850 ft., 10 mi. SW Lawrence, 8; N end Lone
    Star Lake, 9 mi. S, 7 mi. W Lawrence, 1; no specific locality, 6.
    _Ellis County_: 1/2 mi. S, 3-1/2-4 mi. W Hays, 2250 ft., 12.
    _Franklin County_: 4 mi. N Ottawa, 2; 1/2 mi. S, 1-3/4 mi. E Ottawa,
    4. _Gove County_: Castle Rock, 4; no specific locality, 1. _Jackson
    County_: 1/2 mi. N, 3 mi. W Holton, 4. _Leavenworth County_: Ft.
    Leavenworth, 2; no specific locality, 3. _Logan County_: no specific
    locality, 2. _Marshall County_: 2 mi. N, 4 mi. E Oketo, 1; 1/2 mi.
    N, 1-1/2 mi. E Waterville, 1; 1 mi. E Waterville, 5; 1/2 mi. SW
    Waterville, 4. _Mitchell County_: 1/2 mi. S, 3-1/2 mi. W Beloit,
    1500 ft., 4. _Nemaha County_: Nebraska-Kansas line, 7 mi. N Sabetha,
    1; 10-1/2 mi. N Seneca, 1; 2-1/2 mi. S Sabetha, 6. _Norton County_:
    1-1/2 mi. N, 1/4 mi. E Norton, 1; 1/2 mi. N, 4 mi. E Norton, 5; 1
    mi. SW Norton, 10; 4 mi. W, 1 mi. S Logan, 3. _Osage County_: 3 mi.
    N Lyndon, 1. _Osborne County_: 1/2 mi. W Downs, 5. _Phillips
    County_: 2-1/4 mi. SE Long Island, 1. _Pottawatomie County_: 1 mi.
    NW Fostoria, 1. _Rawlins County_: 2 mi. NE Ludell, 17; 2 mi. S
    Ludell, 2; Atwood, 3; Atwood Lake, 2. _Republic County_: 1-1/2 mi.
    S, 1 mi. E Belleville, 1; Rydal, 8. _Scott County_: State Park, 2.
    _Shawnee County_: 1 mi. S Silver Lake, 857 ft., 2. _Sherman County_:
    1/2 mi. S, 1-1/2 mi. E Edson, 1. _Smith County_: 2 mi. E Smith
    Center, 9. _Stafford County_: 16 mi. N, 4 mi. E Stafford, 1. _Thomas
    County_: 10 mi. N, 6 mi. E Colby, 5. _Trego County_: 16 mi. S, 4-1/2
    mi. E Wakeeney, 1. _Wichita County_: 15 mi. W Scott City, 5.

    MONTANA. _Big Horn County_: Big Horn River, 14 mi. S Custer, 2750
    ft., 4. _Dawson County_: 1 mi. W Glendive, 2070 ft., 3. _Phillips
    County_: 1 mi. N, 1 mi. W Malta, 2248 ft., 1. _Powder River County_:
    Powderville, 2900 ft., 1.

    NEBRASKA. _Antelope County_: Neligh, 16 (6 NSM, 9 USNM). _Boyd
    County_: 5 mi. WSW Spencer, 1; 5 mi. S, 2 mi. E Spencer, 2; 6 mi.
    SSE Spencer, 1. _Box Butte County_: Alliance, 2 (USNM). _Buffalo
    County_: Kearney, 2 (USNM). _Burt County_: 1 mi. E Tekamah, 3.
    _Butler County_: 2 mi. N, 2 mi. W Bellwood, 2 (NSM); 4-5 mi. E
    Rising City, 11; 4 mi. E, 1 mi. S Rising City, 5. _Chase County_: 2
    mi. SE Enders, 1. _Cherry County_: W of Crookston, 1 (NSM);
    Valentine, 2 (USNM); Ft. Niobrara Nat'l Wildlife Refuge, 4 mi. E
    Valentine, 5 (3 NSM); 3 mi. SSE Valentine, 4; 3 mi. S Valentine, 12;
    8 mi. S Nenzel, 2; Niobrara River, 10 mi. S Cody, 2 (1 USNM); 11 mi.
    S, 2 mi. W Nenzel, 1; 18 mi. NW Kennedy, 8 (2 NSM, 6 USNM); Two Mile
    Lake, 6 (4 NSM, 2 USNM); Watt's Lake, Valentine Nat'l Wildlife
    Refuge, 3; Hackberry Lake, 12 (UMMZ); 2 mi. W to 4 mi. E Kennedy, 25
    (4 UMMZ, 12 USNM); no specific locality, 1 (USNM). _Cheyenne
    County_: 15 mi. S Dalton, 4300 ft., 1; 3 mi. N Sidney, 6; 4 mi. E
    Sidney, 42. _Cuming County_: Beemer, 1 (USNM). _Custer County_: 7
    mi. NW Anselmo, 1 (UMMZ); within 1 mi. Victoria Spring, 9 (UMMZ); 2
    mi. E Lillian, 1 (UMMZ); Comstock, 1 (NSM); Callaway, 3 (USNM); 6
    mi. SE Mason City, 1 (UMMZ). _Dawes County_: Wayside, 1; 3 mi. E
    Chadron, 2; 6 mi. S Chadron, 1 (NSM); 8 mi. S Chadron, 1 (NSM); 10
    mi. S Chadron, 1 (UMMZ); 1 mi. W Crawford, 2 (NSM); Crawford, 2
    (UMMZ). _Dawson County_: 1/2 mi. S Gothenburg, 5; 3 mi. SSE
    Gothenburg, 4. _Deuel County_: 1 mi. N, 2 mi. W Chappell, 3. _Dixon
    County_: 3 mi. NE Ponca, 4. _Dundy County_: Rock Creek Fish
    Hatchery, 5 mi. N, 2 mi. W Parks, 42; 2 mi. N, 2 mi. W Haigler, 1;
    Arikaree River, Parks, 2; 2 mi. SW Benkleman, 7; Haigler, 3 (1 NSM,
    2 USNM). _Franklin County_: 1-1/2-2 mi. S Franklin, 10. _Gage
    County_: 1 mi. SE DeWitt, 3; 1/4 mi. W Homestead Nat'l Mon., 1; 1
    mi. S, 1 mi. W Barnston, 1; 1-1/2 mi. S, 2 mi. E Barnston, 18.
    _Garden County_: Crescent Lake Nat'l Wildlife Refuge, 1; 1/2 mi. S
    Oshkosh, 1. _Hall County_: 6 mi. S Grand Island, 5. _Harlan County_:
    1 mi. W Alma, 17. _Hitchcock County_: Republican River, Trenton, 3.
    _Hooker County_: Kelso, 3 (UMMZ). _Holt County_: 6 mi. N Midway, 4;
    1 mi. S Atkinson, 4 (2 NSM); Ewing, 1 (USNM). _Jefferson County_: 7
    mi. S, 2 mi. W Fairbury, 6; 3 mi. S, 1 mi. W Endicott, 1. _Johnson
    County_: 1 mi. S, 1-1/2 mi. E Burr, 1. _Kearney County_: 1-3/4-3-3/4
    mi. S Kearney, 6. _Keith County_: 4 mi. WNW Keystone, 69. _Keya Paha
    County_: 12 mi. N Springview, 8; 12 mi. NNW Springview, 5. _Kimball
    County_: 3 mi. E Kimball, 1; Smeed, 40. _Knox County_: 3 mi. W
    Niobrara, 2; 1 mi. SE Niobrara, 5; 2 mi. S Niobrara, 2; Verdigre, 2
    (USNM). _Lancaster County_: within 5 mi. Lincoln, 21 (8 NSM).
    _Lincoln County_: 2 mi. N North Platte, 1; Conroy Canyon, SW corner
    sec. 4, T. 11 N, R. 27 W (5 mi. S, 2-1/2 mi. W Brady), 2 (NSM).
    _Logan County_: 1-2 mi. NE Stapleton, 11. _Madison County_: Norfolk,
    1 (USNM). _Morrill County_: 1 mi. N Bridgeport, 4. _Nemaha County_:
    2 mi. SW Peru, 6; 3 mi. S, 1-1/2 mi. E Peru, 2. _Nuckolls County_: 2
    mi. WSW Superior, 5; 1 mi. SSW Hardy, 9. _Otoe County_: 1 mi. SE
    Nebraska City, 3; 3 mi. S, 2 mi. E Nebraska City, 3. _Pawnee
    County_: Turkey Creek, 4 mi. NW Pawnee City, 2 (NSM); 4 mi. S, 8 mi.
    W Pawnee City, 7; 1 mi. S Du Bois, 4. _Platte County_: Columbus, 3
    (USNM). _Polk County_: 15 mi. W Osceola, 2. _Red Willow County_: 5
    mi. S, 2-1/2 mi. E McCook, 2; 8 mi. S, 3 mi. E McCook, 2.
    _Richardson County_: 5 mi. N, 2 mi. W Humboldt, 2 (1 NSM); 4 mi. E
    Barada, 16; 3-1/2 mi. S, 1 mi. W Dawson, 6; 2 mi. N Falls City, 2;
    4-6 mi. W Falls City, 4; 1/2 mi. S, 1-1/2 mi. W Rulo, 1. _Saline
    County_: 2 mi. NE Crete, 1; 1/2 mi. W DeWitt, 1. _Sarpy County_: 1
    mi. W Meadow, 1. _Saunders County_: 2 mi. NW Ashland, 3. _Scotts
    Bluff County_: 8 mi. NNW Scottsbluff, 1; Mitchell, 1 (NSM); 1/2-1
    mi. S Mitchell, 13; 5 mi. S Gering, 10; 7 mi. S Gering, 1; 11-12 mi.
    S Scottsbluff, 4600-4800 ft., 8; 12 mi. SSW Scottsbluff, 4700 ft.,
    5. _Sioux County_: 1 mi. S, 4 mi. W Orella, 1 (NSM); 8 mi. N
    Harrison, 2 (UMMZ); 6-1/2-7 mi. W Crawford, 3 (1 NSM); 8 mi. N, 1
    mi. E Glen, 1 (NSM); 3 mi. NE Glen, 1 (NSM); Glen, 3 (NSM); Agate,
    4600 ft., 1. _Stanton County_: 1-1/2 mi. S Pilger, 3; 6 mi. SE
    Norfolk, 1. _Thomas County_: 1 mi. W Halsey, 2; Halsey, 1 (NSM).
    _Thurston County_: 1 mi. S Winnebago, 8. _Valley County_: 2 mi. W
    Ord, 1; 2 mi. S, 4 mi. E Ord, 6. _Washington County_: 1 mi. E Blair,
    6; 3 mi. SE Blair, 2; 6 mi. SE Blair, 7; 3 mi. S, 2 mi. E Ft.
    Calhoun, 1 (NSM). _Wayne County_: 1/2 mi. W-2-1/2 mi. E Wayne, 3.
    _Webster County_: 3 mi. S Red Cloud, 2.

    SOUTH DAKOTA. _Buffalo County_: 2 mi. S, 3 mi. E Ft. Thompson, 1370
    ft., 4. _Clay County_: 2-1/2 mi. N, 1/2 mi. W Vermillion, 1.
    _Pennington County_: 2 mi. S, 3 mi. W Scenic, 1. _Stanley County_:
    1.2 mi. S, 4 mi. W Ft. Pierre, 1484 ft., 1.

    WYOMING. _Albany County_: 27 mi. N, 8 mi. E Laramie, 6420 ft., 2.
    _Big Horn County_: 7-1/2 mi. E Graybull, 4050 ft., 1; 7 mi. S, 1/2
    mi. E Basin, 3900 ft., 1. _Campbell County_: 4 mi. N, 3 mi. E
    Rockypoint, 3800 ft., 3; 1-3/5 mi. N, 3/4 mi. E Rockypoint, 2;
    Rockypoint, 5; 5 mi. S, 4 mi. W Rockypoint, 1; Ivy Creek, 5 mi. N, 8
    mi. W Spotted Horse, 2. _Crook County_: 1-1/2 mi. NW Sundance, 5000
    ft., 3. _Fremont County_: 2 mi. N, 3 mi. W Shoshoni, 4650 ft., 1;
    3/10 mi. NW Milford, 5357 ft., 1; Milford, 5400 ft., 1. _Hot Springs
    County_: 3 mi. N, 10 mi. W Thermopolis, 4900-4950 ft., 7. _Johnson
    County_: 1 mi. W, 8/10 mi. S Buffalo, 4800 ft., 5; 6-1/2 mi. W, 2
    mi. S Buffalo, 5620 ft., 4; 1 mi. WSW Kaycee, 4700 ft., 8. _Laramie
    County_: Horse Creek, 5000 ft., 3 mi. W Meriden, 1; 1 mi. N, 1/2 mi.
    W Pine Bluffs, 5040 ft., 4; 1 mi. S Pine Bluffs, 5100 ft., 1; 2 mi.
    S Pine Bluffs, 5200 ft., 2. _Natrona County_: 1 mi. NE Casper, 5150
    ft., 1; 2-1/4 mi. W Casper, 5250 ft., 1; 7 mi. S, 2 mi. W Casper,
    6370 ft., 1. _Niobrara County_: 2 mi. S, 1/2 mi. E Lusk, 5000 ft.,
    1. _Park County_: 4 mi. N Garland, 2; 13 mi. N, 1 mi. E Cody, 5200
    ft., 2; 6/10 mi. S, 3-2/10 mi. E Cody, 5020 ft., 1. _Platte County_:
    2-1/2 mi. S Chugwater, 5300 ft., 4. _Sheridan County_: 3 mi. WNW
    Monarch, 3800 ft., 4; 5 mi. NE Clearmont, 3900 ft., 6. _Washakie
    County_: 1 mi. N, 3 mi. E Tensleep, 4350 ft., 5.


TABLE 2. CRANIAL MEASUREMENTS OF TWO SUBSPECIES OF REITHRODONTOMYS
MEGALOTIS.

Key to Table Headings:

A =NUMBER AVERAGED AND SEX
B = Greatest length of skull
C = Zygomatic breadth
D = Breadth of braincase
E = Interorbital breadth
F = Depth of cranium
G = Length of rostrum
H = Breadth of rostrum
I = Length of incisive foramen
J = Length of palate
K = Alveolar length of maxillary tooth-row
--------------------------+----+----+----+---+---+---+---+---+---+----
          A               | B  | C  | D  | E | F | G | H | I | J |  K
--------------------------+----+----+----+---+---+---+---+---+---+----
_R. m. dychei_, Douglas County, Kansas

Av. 17 (11 male, 6 female)|20.9|10.5|10.1|3.1|7.9|7.2|3.8|4.3|3.5|3.3
Minimum                   |20.4|10.0| 9.8|3.0|7.7|6.8|3.6|4.0|3.2|3.1
Maximum                   |21.9|10.9|10.3|3.3|8.2|7.9|4.0|4.5|3.9|3.4
--------------------------+----+----+----+---+---+---+---+---+---+----
Cherry County, Nebraska

Av. 20 (14 male, 6 female)|21.0|10.9|10.3|3.1|7.9|7.3|3.8|4.4|3.6|3.5
Minimum                   |20.4|10.0| 9.8|2.9|7.5|6.8|3.5|4.3|3.4|3.2
Maximum                   |22.1|11.3|10.7|3.3|8.4|7.8|4.1|4.7|3.9|3.7
--------------------------+----+----+----+---+---+---+---+---+---+----
_R. m. aztecus_, San Juan County, New Mexico, and Montezuma County,
Colorado

Av. 10 (6 male, 4 female) |21.5|10.8|10.2|3.1|8.1|7.7|3.7|4.5|3.4|3.5
Minimum                   |20.5|10.4| 9.9|2.9|7.9|7.2|3.5|3.9|3.1|3.2
Maximum                   |22.7|11.1|10.6|3.3|8.4|8.2|3.9|4.8|3.7|3.7
--------------------------+----+----+----+---+---+---+---+---+---+----




LITERATURE CITED


ALLEN, J. A.

    1893. List of mammals collected by Mr. Charles P. Rowley in the San
          Juan region of Colorado, New Mexico and Utah, with
          descriptions of new species. Bull. Amer. Mus. Nat. Hist,
          5:69-84, April 28.

    1895. On the species of the genus Reithrodontomys. Bull. Amer. Mus.
          Nat. Hist, 7:107-143, May 21.

BENSON, S. B.

    1935. The status of Reithrodontomys montanus (Baird). Jour. Mamm.,
          16:139-142, 1 fig., May 15.

BLAIR, W. F.

    1954. Mammals of the Mesquite Plains Biotic District in Texas and
          Oklahoma, and speciation in the central grasslands. Texas
          Jour. Sci., 6:235-264, 1 fig., September.

DALQUEST, W. W.

    1948. Mammals of Washington. Univ. Kansas Publ., Mus. Nat. Hist.,
          2:1-444, 140 figs., April 9.

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

    1959. The mammals of North America. Ronald Press, New York, vols.
          1:xxx + 1-546 + 79 and 2:viii + 547-1083 + 79, 553 figs., 500
          maps, 178 unnumbered text figs., March 31.

HILL, J. E., and C. W. HIBBARD

    1943. Ecological differences between two harvest mice
          (_Reithrodontomys_) in western Kansas. Jour. Mamm., 24:22-25,
          February 20.

HOFFMEISTER, D. F., and J. E. WARNOCK

    1955. The harvest mouse (Reithrodontomys megalotis) in Illinois and
          its taxonomic status. Trans. Illinois Acad. Sci., 47:161-164,
          1 fig.

HOOPER, E. T.

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

HOWELL, A. H.

    1914. Revision of the American harvest mice (genus Reithrodontomys).
          N. Amer. Fauna, 36:1-97, 7 pls., 6 figs., June 5.

    1935. The harvest mice of the San Luis Valley, Colorado. Jour.
          Mamm., 16:143-144, May 15.

LAYNE, J. N.

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

VERTS, B. J.

    1960. Ecological notes on _Reithrodontomys megalotis_ in
          Illinois. Nat. Hist. Misc., Chicago Acad. Sci., 174:1-7, 1
          fig., July 25.


_Transmitted March 30, 1961._