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._ 23-7439 --- Provided by LoyalBooks.com ---