Thomomys bottae contractus new subspecies
Thomomys perpallidus albicaudatus Hall, Univ. California Publ. Zoöl., 37:3, April 10, 1931.
Thomomys bottae albicaudatus Durrant. Bull. Univ. Utah, 28 (No. 4):4, August 18, 1937.
Type.—Male, adult, skin and skull, No. 1851, Museum of Zoölogy, University of Utah; Scipio, 5,315 ft., Millard County, Utah; September 17, 1936; collected by S. D. Durrant; original number 1125.
Range.—Extreme eastern Millard and Beaver counties, Utah.
Diagnosis.—Size medium (see measurements). Color: Upper parts Cinnamon Buff, mixed with black giving a color of Dresden Brown; sides between Cinnamon Buff and Pinkish Buff; underparts Pinkish Buff, purest on inguinal and pectoral regions; postauricular patches medium in size and black; ears covered with black hairs; nose, chin, cheeks and top of head dusky; front feet, hind feet and distal third to half of tail white; proximal part of tail covered all around with buff-colored hairs. Skull: Long, slender, moderately ridged and convex transversally at proximal ends of nasals; nasals long; rostrum long and narrow; posterior ends of nasals truncate or shallowly emarginate; ascending processes of premaxillae slender; extension of premaxillae posterior to nasals long; zygomatic arches neither robust nor widely spreading; interparietal subquadrangular; supraoccipital extending horizontally well behind lambdoidal suture instead of dropping off abruptly to the foramen magnum; interpterygoid space moderately V-shaped in some specimens, but somewhat lyre-shaped in others; tympanic bullae large and truncate anteriorly; upper incisors long and narrow; molariform teeth small and light.
Comparisons.—Compared with topotypes of Thomomys bottae albicaudatus, contractus differs as follows: Tail longer. Color: Lighter throughout. Skull: Slenderer, less ridged and angular; rostrum narrower; zygomatic and mastoidal breadths less; ascending processes of premaxillae narrower; posterior tongues of premaxillae narrower; posterior ends of nasals less truncate; zygomatic arches weaker, less angular, and less widely spreading posteriorly; interparietal larger; paroccipital processes weaker; interpterygoid space not as widely V-shaped; upper incisors longer and narrower; molariform teeth smaller.
Topotypes of contractus can be distinguished from those of Thomomys bottae convexus by the following: Size larger, tail longer; hind foot larger. Color: Darker throughout. Skull: Longer, narrower, and not as massive; top of skull moderately, as opposed to strongly, convex; nasals arched rather than straight; zygomatic arches neither as widely spreading, angular nor massive; space enclosed within zygomatic arches longer; interparietal larger; interpterygoid space more narrowly V-shaped; upper incisors longer and narrower; molariform teeth much lighter.
Comparisons of topotypes of contractus with near topotypes of Thomomys bottae centralis show them to be approximately the same size, but to differ as follows: Color: Darker throughout. Skull: Shorter and slenderer; rostrum narrower; region between posterior tongues of premaxillae narrower and more convex transversally; nasals more truncate; zygomatic breadth less, but arches relatively more widely spreading posteriorly; interparietal larger; interpterygoid space generally narrower; upper incisors longer and narrower; molariform teeth smaller.
Topotypes of contractus differ from those of Thomomys bottae aureiventris as follows: Size smaller; tail longer; hind foot shorter. Color: Darker throughout. Skull: Shorter but slenderer; rostrum narrower; nasals shorter but slenderer, and more truncate posteriorly; extension of premaxillae posterior to nasals longer; zygomatic arches weaker and less angular; zygomatic processes of maxillae weaker and with no marked thickenings at union of maxilla and jugals; interparietal larger; interpterygoid space more generally V-shaped; upper incisors longer and narrower; molariform teeth smaller.