Part 2

The pale color of the animals belonging to C. c. pallidus was noted at the time of capture, and is the same in the young specimen (625 mm. total length) as in the type, an adult.

Specimens examined.--Total, 2, distributed as follows: Boxelder County: Raft River, 5 mi. S Yost, Raft River Mountains, 6,000 ft., 1; Lynn Canyon, Raft River Mountains, 7,500 ft., 1.

~Castor canadensis rostralis~ new subspecies

Type.--Male, young adult, skin and skull, number 5199, Museum of Zoology, University of Utah; Red Butte Canyon, Fort Douglas, 5,000 ft., Salt Lake County, Utah; October 13, 1947; collected by Harold S. Crane and Clifton M. Greenhalgh, original number 446 of Crane.

Range.--Known from the western streams of the Wasatch Mountains; probably occurs in all streams draining westward into the basin of Pleistocene Lake Bonneville.

Diagnosis.--Size large; tail and hind foot long (see measurements). Color (type): Upper parts Snuff Brown, purest on head; underfur Brownish Black (2); base of tail Cinnamon Buff; hind feet Carob Brown; ears Blackish Brown (2); underparts Auburn, grading posteriorly to Cinnamon Buff; underfur Light Drab. Skull: Large, massive; nasals short and broad (breadth averaging 54 per cent of length) and moderately convex transversely; rostrum deep and broad; ventral surface of rostrum moderately concave dorsally; dorsal surface of lacrimal bone small; frontal region generally flat; zygomatic arches robust and widely spreading (zygomatic breadth averaging 82 per cent of basilar length).

Measurements.--Measurements of the type and average and extreme cranial measurements of 6 unsexed adults from Charleston, are, respectively, as follows: Total length, 1,330; length of tail, 470; length of hind foot, 170; length of ear, 34; occipitonasal length, 128.2, 134.3 (142.1-129.5); basilar length, 112.4, 117.2 (128.2-113.2); mastoid breadth, 62.5, 64.3 (68.9-60.2); interorbital breadth, 27.9, 26.0 (26.9-26.0); zygomatic breadth, 91.3, 93.8 (105.8-90.8); length of nasals, 44.9, 43.9 (51.3-41.5); breadth of nasals, 24.5, 23.7 (25.7-22.0); alveolar length of upper molariform teeth, 28.3, 30.9 (32.5-28.7).

Comparisons.--From topotypes and near topotypes of Castor canadensis taylori, C. c. rostralis differs as follows: Color: Darker on upper parts owing to darker underfur, guard hairs actually lighter. Skull: Longer; nasals shorter and wider (breadth of nasals averages 54 per cent of length of nasals as opposed to 47 per cent); extension of nasals posterior to premaxillae less; rostrum shorter, broader and deeper; dorsal surface of lacrimal bone smaller; zygomatic breadth relative to basilar length greater; mastoid breadth relative to zygomatic breadth less; coronoid process shorter; coronoid and condyloid processes farther apart and space between them shallower.

From one topotype and two specimens from the Colorado River at Yuma, Yuma County, Arizona, of Castor canadensis repentinus, C. c. rostralis differs as follows: Size larger; tail longer. Color: Darker throughout. Skull: Longer; nasals shorter and wider (breadth of nasals relative to length of nasals averages 54 per cent as opposed to 47 per cent); extension of nasals posterior to premaxillae less; rostrum shorter, deeper and wider; zygomatic breadth relative to basilar length greater; mastoid breadth actually as well as relatively greater; dorsal surface of lacrimal bone smaller; coronoid and condylar processes farther apart and space between them shallower.

From specimens of Castor canadensis baileyi, from 20 miles north northeast of Elko, Elko County, Nevada, C. c. rostralis differs as follows: Size larger; tail and hind foot longer. Color: Darker throughout. Skull: Larger in all measurements taken; nasals markedly wider (breadth of nasals relative to length of nasals averages 54 per cent as opposed to 41 per cent); extension of nasals posterior to premaxillae less; dorsal surface of lacrimal bone smaller; mastoid breadth relative to zygomatic breadth less.

From one specimen of Castor canadensis concisor, from Trappers Lake, Garfield County, Colorado, and from the original description of that subspecies (Warren and Hall, 1939: 358), C. c. rostralis differs as follows: Color: Guard hairs lighter; underfur darker (blackish as opposed to brownish). Skull: Longer and narrower; nasals broader and shorter (breadth of nasals averages 54 per cent of length of nasals as opposed to 48 per cent); dorsal surface of lacrimal bone smaller; distal end of meatal tube smaller; distal end of angular process rounded rather than pointed; coronoid process shorter; coronoid and condylar processes farther apart and space between them shallower.

Among known kinds of Castor canadensis, C. c. rostralis is most like Castor canadensis duchesnei, from which the former subspecies differs as follows: Tail and hind foot longer. Color: Darker throughout. Skull: Nasals shorter and wider (breadth of nasals averages 54 per cent of length of nasals as opposed to 46 per cent); nasals less arched transversely; rostrum shorter, deeper and broader; ventral surface of rostrum less concave dorsally; dorsal surface of lacrimal bone smaller.

For comparison with Castor canadensis pallidus, see account of that subspecies.

Remarks.--Animals from Kamas, in the drainage of the Weber River, are intergrades between C. c. rostralis and C. c. duchesnei, but their short, wide nasals and wide rostra make them referable to C. c. rostralis.

The available specimens of C. c. rostralis are all from streams which ultimately empty into Great Salt Lake, which is in the northern part of the basin of Pleistocene Lake Bonneville. Some streams drain into the Lake Bonneville Basin without emptying into Great Salt Lake proper. Beavers from these streams, we suspect, when they become known, will be found to be related to C. c. rostralis.

Specimens examined.--Total, 16 (2 skins and skulls, 14 skulls only), distributed as follows: Summit County: Kamas, 5,500 ft., 6. Salt Lake County: Red Butte Canyon, Fort Douglas, 5,000 ft., 1; Millcreek Canyon, 6 mi. above mouth, 7,000 ft., 1. Wasatch County: Charleston, Heber Valley, 5,500 ft., 8.

~Castor canadensis duchesnei~ new subspecies

Type.--Male, young adult, skin and skull, number 4625, Museum of Zoology, 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).

FIG. 1. Castor canadensis rostralis, male, young adult, no. 5199 (holotype), Mus. Zool., Univ. Utah.

FIG. 2. Castor canadensis pallidus, female, adult, no. 719 (holotype), Mus. Zool., Univ. Utah.

FIG. 3. Castor canadensis duchesnei, male, young adult, no. 4625 (holotype), Mus. Zool., Univ. Utah.

FIG. 4. Castor canadensis concisor, male, adult, no. 2090, Mus. Nat. Hist., Univ. Kansas, from Trappers Lake, Garfield County, Colorado, obtained by L. L. Dyche, October 22, 1891.

Comparisons.--From topotypes and near topotypes of Castor canadensis taylori, C. c. duchesnei differs as follows: Color: Guard hairs lighter, underfur darker. Skull: Nasals narrower; rostrum narrower; mastoid breadth relative to zygomatic breadth less; zygomatic breadth relative to basilar length greater; tympanic bullae narrower and smaller; cheek teeth narrower.

Fig. 5. Castor canadensis rostralis, male, young adult, no. 5199 (holotype), Mus. Zool., Univ. Utah.

Fig. 6. Castor canadensis pallidus, female, adult, no. 719 (holotype), Mus. Zool., Univ. Utah.