Castor canadensis duchesnei new subspecies
Type.—Male, young adult, skin and skull, number 4625, Museum of Zoölogy, University of Utah; Duchesne River, 10 miles northwest of Duchesne, 5,600 ft., Duchesne County, Utah; September 23, 1946; collected by Dave Thomas, original number 160 of K. R. Kelson.
Range.—Drainage of the Duchesne and White rivers in Utah and Colorado.
Diagnosis.—Size large; tail long (see measurements). Color (type): Upper parts Sayal Brown, purest on head, grading to Cinnamon Buff at base of tail; underfur Fuscous; hind feet Burnt Umber; ears Fuscous Black; underparts Tawny Olive; underfur Smoke Gray. Skull: Large, massive; nasals long, slender (breadth averaging 46 per cent of length) and markedly convex transversely; rostrum long and attenuate; zygomatic arches heavy and widely spreading (zygomatic breadth averaging 81.5 per cent of basilar length); ventral surface of rostrum markedly concave dorsally, especially immediately behind upper incisors; nasals extend posterior to premaxillae.
Measurements.—Measurements of the type and average and extreme cranial measurements of 9 unsexed adults, from Currant Creek, are, respectively, as follows: Total length, 1,176; length of tail, 458; length of hind foot, 165; length of ear, 33; occipitonasal length, 123.6, 132.1 (138.5-122.3); basilar length, 98.6, 114.4 (125.8-99.2); mastoid breadth, 60.4, 65.1 (67.2-64.1); interorbital breadth, 23.0, 25.1 (26.1-23.7); zygomatic breadth, 88.3, 94.2 (99.7-89.5); length of nasals, 46.1, 48.4 (51.5-46.2); breadth of nasals, 20.5, 22.5 (24.5-18.8); alveolar length of upper molariform teeth, 28.9, 29.9 (32.2-26.5).
Figs. 1-4 Dorsal views of skulls of Castor canadensis. × 1/2
Fig. 1. Castor canadensis rostralis, male, young adult, no. 5199 (holotype), Mus. Zoöl., Univ. Utah.
Fig. 2. Castor canadensis pallidus, female, adult, no. 719 (holotype), Mus. Zoöl., Univ. Utah.
Fig. 3. Castor canadensis duchesnei, male, young adult, no. 4625 (holotype), Mus. Zoöl., Univ. Utah.