A New Pocket Gopher (Genus Thomomys), from Eastern Colorado — Text and Context

A Nomenclatural Puzzle Unpacked

The opening paragraphs do not leap directly into description. Instead, Hall first lays out a taxonomic problem: pocket gophers from east-central Colorado had long been assigned to Thomomys talpoides clusius, a subspecies whose type locality is Bridger Pass, Wyoming, over 200 miles away. By 1951, two newly named subspecies—T. t. attenuatus and T. t. rostralis—had been described from the Wyoming-Colorado border, geographically separating the Colorado populations from T. t. clusius. Hall then explains that he examined specimens expecting to apply the names T. t. macrotis or T. t. cheyennensis, but found neither fit. This step-by-step reasoning reveals how taxonomic decisions were made through elimination and geographic logic, not just by comparing physical traits.

The Type Specimen and Its Provenance

Hall designates a single type specimen: a subadult male, catalog number 69840 in the Biological Surveys Collection of the U.S. National Museum. It was collected on November 26, 1894, by Clark P. Streator at Flagler, Kit Carson County, Colorado. The specimen consists of both skull and skin, standard for mammalian taxonomy at the time. Hall also provides a range for the new subspecies: "the western end of the Arkansas Divide in Colorado from eight miles south of Seibert westward to Colorado Springs." This geographic delimitation is precise, tying the subspecies to a specific physiographic feature. The paper does not explain why only one type specimen was used, nor does it discuss population variation beyond the diagnosis.

Cranial and Pelage Characters in the Diagnosis

The diagnosis is brief and technical. Hall describes the new subspecies as having "size medium," upper parts "grayish brown," and lighter underparts. The skull is characterized as small, with "tympanic bullae moderately inflated and angular anterolaterally," an "interpterygoid space narrowly U-shaped," and pterygoid hamuli without transverse processes. These features distinguish T. t. retrorsus from related forms. Notably, the diagnosis does not include measurements in the excerpt, though the full paper likely contains a table. The language is spare and functional, aimed at specialists who would compare specimens under a microscope. No illustrations are mentioned in the excerpt, but the text implies that visual inspection of skull morphology was central to the identification.

Readers should note that this paper is a primary taxonomic source, not a general natural history. It assumes familiarity with gopher anatomy and the subspecies concept. The excerpt includes only the introduction and diagnosis; the full work contains measurements and a discussion of comparisons. For those interested in how species were defined before molecular tools, Hall's method—relying on geographic isolation and subtle morphological differences—offers a clear example of mid-century practice.

That rainy afternoon, I kept returning to Hall’s careful measurements of pocket gopher skulls—such devotion to tiny differences. It made me wonder about the illustrators who first tried capturing animals nobody had named yet. Later, idly, I found Zoological Illustrations, Volume 3 or, Original Figures and Descriptions of New, Rare, or Interesting Animals — Edition Insights, and the same patient wonder was there, only in color.