Thomomys bottae sevieri new subspecies
Type.—Female, adult, skin and skull, No. 2530, Museum of Zoölogy, University of Utah; Swasey Spring, House Mountains, 6,500 ft., Millard County, Utah; May 16, 1938; collected by S. D. Durrant; original number 1380.
Range.—Known only from the type locality.
Diagnosis.—Size medium (see measurements); claws on front feet short and weak; ears short; tail relatively long. Color: Upper parts Pinkish Buff, grading over sides to Pale Pinkish Buff on underparts; nose, top of head, chin and cheeks grayish black; postauricular patches small and grayish black; front and hind feet and distal two-thirds of tail white. Skull: Small, weak and smooth; rostrum narrow; nasals narrow, not markedly flared distally; zygomatic arches weak, not angular, and of "graceful" contour; lacrimal processes small; characteristic dorsal depression present in region of sagitto-coronal suture; mastoid and zygomatic breadths narrow; occiput narrow and high; braincase well inflated; paroccipital processes small and smooth; interpterygoid space narrowly V-shaped; tympanic bullae small, but well inflated ventrally; alveolar length of upper molar series short; molars small; upper incisors short, but narrow.
Comparisons.—From topotypes of Thomomys bottae aureiventris, sevieri differs as follows: Size smaller. Color: Lighter throughout, no "gold" on underparts. Skull: Much smaller in every measurement taken, less massive and not angular; zygomatic arches weaker and widest posteriorly rather than anteriorly; union of jugal and zygomatic process of maxilla not greatly thickened; interpterygoid space narrowly V-shaped rather than lyre-shaped; pterygoid hamulae shorter and weaker; tympanic bullae smaller, but markedly more inflated ventrally; dentition smaller and weaker.
From near topotypes of Thomomys bottae centralis, sevieri can be distinguished by the following features: Size markedly smaller. Color: Lighter throughout. Skull: Markedly smaller in every measurement taken, weaker and smoother; zygomatic arches weaker, less angular and more "graceful"; rostrum shorter, but narrower; lacrimal processes smaller; tympanic bullae smaller, but more inflated ventrally, being triangular in shape as opposed to ovate and with anteromedial margin decidedly pointed; pterygoid hamulae smaller and weaker; dentition smaller and weaker.
T. b. sevieri can readily be distinguished from Thomomys bottae albicaudatus by the following features: Size smaller in every measurement taken. Color: Markedly lighter throughout. Skull: Smaller, and weaker; rostrum shorter and narrower; ascending processes of premaxillae narrower; extension of premaxillae posterior to nasals shorter; posterior tongues of premaxillae narrower; dentition much lighter.
Comparisons of sevieri with topotypes of Thomomys bottae wahwahensis show them to be of approximately the same size, but to differ as follows: Hind foot longer; ear shorter. Color: Slightly darker. Skull: Smaller, weaker, less ridged; zygomatic breadth less; zygomatic arches markedly less angular; mastoid breadth less; rostrum much longer and narrower, not as blunt nor flattened; tympanic bullae much larger and more inflated ventrally; braincase vaulted as opposed to flattened.
From topotypes of Thomomys bottae bonnevillei, sevieri differs in: Size smaller throughout. Skull: Smaller in every measurement taken, weaker, smoother and less angular; dentition smaller and weaker.