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                 A New Pocket Gopher (Genus Thomomys)
                        from Eastern Colorado

                                  BY

                           E. RAYMOND HALL


                  University of Kansas Publications
                      Museum of Natural History

                      Volume 5, No. 8, pp. 81-85
                           October 1, 1951


                         University of Kansas
                               LAWRENCE
                                 1951




     UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

        Editors: E. Raymond Hall, Chairman, A. Byron Leonard,
                  Edward H. Taylor, Robert W. Wilson

                      Volume 5, No. 8, pp. 81-85
                           October 1, 1951


                         UNIVERSITY OF KANSAS
                           Lawrence, Kansas


                              PRINTED BY
                   FERD VOILAND, JR., STATE PRINTER
                            TOPEKA, KANSAS
                                 1951

                               23-7439




                 A New Pocket Gopher (Genus Thomomys)
                        from Eastern Colorado

                                  By

                           E. RAYMOND HALL


The pocket gophers of the species _Thomomys talpoides_ in east-central
Colorado have long been referred to the subspecies _Thomomys talpoides
clusius_ Coues with type locality at Bridger Pass, Wyoming. Recently,
two subspecies, _T. t. attenuatus_ and _T. t. rostralis_ (see Hall and
Montague, Univ. Kansas Publ., Mus. Nat. Hist., 5(3):25-32, February 28,
1951) were named from along the Wyoming-Colorado boundary with the
result that the populations of _Thomomys talpoides_ in east-central
Colorado are separated from _T. t. clusius_ of Wyoming by the geographic
ranges now ascribed to the recently named _T. t. attenuatus_ and _T. t.
rostralis_. The subspecific identity of the animals from east-central
Colorado thus is left in doubt. Examination of pertinent materials was
made in the expectation that the names _Thomomys talpoides macrotis_ F.
W. Miller (Proc. Colorado Mus. Nat. Hist., 9:41, December 14, 1930) and
_Thomomys talpoides cheyennensis_ Swenk (Missouri Valley Fauna, 4:5,
March 1, 1941) would apply to the specimens, the identity of which is in
doubt. This examination discloses instead, as set forth in more detail
below, that neither of the two names mentioned immediately above does
apply; the Coloradan specimens in question are referable to an
heretofore unrecognized subspecies which may be named and described as
follows:

          #Thomomys talpoides retrorsus# new subspecies

      _Thomomys clusius_, Warren, The Mammals of Colorado,
          G. P. Putnam's Sons, New York, p. 80, 1910;
          Cary, N. Amer. Fauna, 33:132, August 17, 1911.

      _Thomomys talpoides clusius_, Bailey, N. Amer. Fauna,
          39:100, November 15, 1915; F. W. Miller, Proc.
          Colorado Mus. Nat. Hist., 9:41, December 14, 1930;
          Warren, The Mammals of Colorado, Univ. Oklahoma
          Press, Norman, p. 162, 1942.

    _Type._--Male, subadult, skull and skin, No. 69840 Biological
    Surveys Collection, U. S. Nat. Hist.; from Flagler, Kit Carson
    County, Colorado; obtained on November 26, 1894, by Clark P.
    Streator; original No. 4460.

    _Range._--Western end of the Arkansas Divide in Colorado from
    eight miles south of Seibert westward to Colorado Springs

    _Diagnosis._--Size medium (see measurements); upper parts
    grayish brown; underparts lighter; skull small; tympanic bullae
    moderately inflated and angular anterolaterally; interpterygoid
    space narrowly U-shaped; pterygoid hamuli without transverse
    enlargement; nasals truncate posteriorly; premaxillary tongues
    projecting posteriorly behind nasals for distance of
    eight-tenths (0.5-1.1) of a millimeter.

    _Comparisons._--In comparison with _T. t. fossor_ and _T. t.
    rostralis_, which occur farther west, selected differences of
    _T. t. retrorsus_ are: lighter color; larger skull; more
    inflated tympanic bullae; greater relative (to length of skull)
    breadth across upper incisors, rostrum, and zygomata. The
    difference in color is greater in comparison with _fossor_ than
    with _rostralis_.

    In comparison with _T. t. macrotis_ (specimens from the type
    locality), _T. t. retrorsus_ is indistinguishable in color,
    length of tail, and length of tooth-row, but averages smaller in
    all other measurements. There is no overlap in length of body,
    basilar length, zygomatic breadth, mastoidal breadth or length
    of nasals. The temporal ridges, which mark the limits of the
    temporal muscles, are straight as opposed to curved and are
    lower. The tympanic bullae are more angular anterolaterally in
    _T. t. retrorsus_.

    From _T. t. attenuatus_ to the north, _T. t. retrorsus_ differs
    in darker (more brown) color, consistently longer body,
    relatively (to length of skull) shorter rostrum and nasals.
    Linear measurements of the two latter structures and length of
    tail are approximately the same in the two subspecies but all
    other measurements average more in _T. t. retrorsus_. Also in
    the latter the temporal lines are approximately parallel instead
    of being bowed outward in their middle extent and instead of
    being more widely separated posteriorly than anteriorly.

    From _T. t. cheyennensis_ to the northeast, _T. t. retrorsus_
    differs in slightly darker (more brownish) color, consistently
    shorter body and rostrum, usually a more narrowly V-shaped
    interpterygoid space, and smaller average dimensions of the
    skull, notably in mastoidal breadth and length of the rostrum.

_Remarks._--Miller's (Proc. Colorado Mus. Nat. Hist., 9:42, December 14,
1930) mention of a specimen taken on November 9, 1930, "near the head
of Beaver Creek in extreme northeastern Elbert County" refers to the
specimen, No. 2426 Colo. Mus. Nat. Hist., which is labeled as "8 mi. N.
E. Agate, Elbert Co., Colo." Specimens from Colorado Springs, in the
collection of the late E. R. Warren, have not been examined but the fact
that Cary, Warren 1942, and Bailey (see under synonymy above) each
referred the specimens to _clusius_ instead of to the darker _fossor_
gives basis for tentatively referring the specimens to _T. t.
retrorsus_.

Grateful acknowledgment is made to those persons in charge of the mammal
collections of the Denver Museum of Natural History and the Biological
Surveys collection of mammals in the United States National Museum for
permission to examine and report upon the material listed below (see
specimens examined). The study here reported upon was aided also by a
contract between the Office of Naval Research, Department of the Navy,
and the University of Kansas (NR 161-791). Essential comparative
materials were obtained with assistance from the Kansas University
Endowment Association.

    _Measurements._--Measurements of the type, a male, are followed
    by the measurements of three adult females (69835, 69839 and
    69838) from the type locality. Total length, 216, 207, 210, 200;
    length of tail, 59, 58, 64, 56; length of hind foot, 28, 28, 28,
    26; basilar length of skull, 32.8, 32.2, 32.3, 30.8; zygomatic
    breadth, 23.1, 22.5, ----, 20.5; least interorbital breadth,
    6.0, 6.7, 6.2, 6.1; mastoidal breadth, 18.2, 18.8, 17.7, 17.7;
    length of nasals, 13.0, 13.7, 13.9, 14.0; breadth of rostrum,
    7.6, 7.9, 7.4, 7.2; length of rostrum, 14.8, 15.6, 15.7, 16.0;
    alveolar length of maxillary tooth-row, 7.6, 7.2, 7.7, 7.6.

    _Specimens examined._--Total number, 13, all from Colorado, as
    follows: _Elbert County_ (Colorado Mus. Nat. Hist. [= Denver
    Mus. Nat. Hist.]): Bijou Creek, "near El Paso Co. line", 3;
    8 mi. NE Elbert, 1. _Lincoln Co._ (U. S. Biol. Surv. Coll.):
    Limon, 1. _Kit Carson Co._ (U. S. Biol. Surv. Coll.): Flagler,
    7; 8 mi. S Seibert, 1.

  _Transmitted, February 28, 1951._


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