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. duchesnei_ differs as follows: Color: Lighter throughout. Skull: Nasals more convex transversely; rostrum narrower; ventral border of rostrum more concave dorsally, especially immediately behind upper incisors; distal end of meatal tube smaller; angular process shorter and rounded rather than pointed; cheek teeth smaller. 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.