Among known subspecies of Castor canadensis, C. c. duchesnei is most like Castor canadensis repentinus, but differs from the latter as follows: Size larger; hind foot shorter. Color: Darker throughout. Skull: Basilar length less; mastoid breadth greater; nasals shorter and narrower; extension of nasals posterior to premaxillae less; nasals more convex transversely; cheek teeth smaller.
For comparisons with Castor canadensis pallidus and Castor canadensis rostralis, see accounts of those subspecies.
Remarks.—The extent of the range of C. c. duchesnei within the drainage of the White River is not definitely known. Three animals from 9-1/2 miles southwest of Pagoda Peak, Rio Blanco County, Colorado, from the drainage of the White River, are intergrades between C. c. concisor and C. c. duchesnei. They are like the latter subspecies in shape and length of the nasals, less expanded distal end of the meatal tube and the rounded angular process, and it appears best, pending the acquisition of more material, to refer them to C. c. duchesnei. Another specimen, number 2090, Museum of Natural History, University of Kansas, from Trappers Lake, Garfield County, Colorado, at the headwaters of the White River, and only 16 miles distant from the three aforementioned animals, is, however, nearly typical of C. c. concisor. Relying upon the original description (Warren and Hall, 1939: 358), this animal is like C. c. concisor in size and shape of the jugals, in size of the distal end of the meatal tube and in the pointed end of the angular process. Warren and Hall (loc. cit.) noted that animals assignable to C. c. concisor occurred throughout the mountainous parts of Colorado, and recorded them from the headwaters of nearly all the major rivers of that state. Apparently C. c. concisor also occurs in the headwaters of the White River, while the main part of the river is inhabited by animals referable to C. c. duchesnei.
Specimens examined.—Total, 15 (4 skins and skulls, 11 skulls only), distributed as follows: Utah: Wasatch County: Currant Creek, Strawberry Valley, 6,000 ft., 11. Duchesne County: Duchesne River, 10 mi. NW Duchesne, 5,600 ft., 1. Colorado: Rio Blanco County: 9-1/2 mi. SW Pagoda Peak, 7,700 ft., 3 (Museum of Natural History, University of Kansas).
LITERATURE CITED
Davis, William B.
1939. The Recent mammals of Idaho. The Caxton Printers, Caldwell, Idaho, 400 pp., 2 full page half-tones, 33 figs. in text, April 5, 1939.
Presnall, C. C.