_Diagnosis._--Size small; tail and hind foot short (see measurements). Color (type): Pale, upper parts uniformly Ochraceous-Buff; underfur Snuff Brown; underparts uniformly Light Buff, grading to Light Ochraceous-Buff at base of tail; underfur Light Drab; front and hind feet Light Ochraceous-Buff. Skull: Rostrum short; nasals broad (breadth averaging 54 per cent of length), constricted posteriorly and barely projecting posteriorly beyond premaxillae; zygomatic arches robust, but not widely spreading (zygomatic breadth 77 per cent of basilar length); mastoid breadth 73 per cent of zygomatic breadth; anterolateral margin of orbit narrow (6.2); occipital condyles visible from dorsal view; condylobasal length greater than occipitonasal length; upper incisors narrow (Orange Chrome in color); coronoid processes high and wide; cheek teeth narrow. _Measurements._--Measurements of the type are as follows: Total length, 1040; length of tail, 380; length of hind foot, 157; length of ear, 35; occipitonasal length, 129.1; basilar length, 116.6; mastoid breadth, 65.6; interorbital breadth, 23.6; length of nasals, 43.3; zygomatic breadth, 89.7; breadth of nasals, 23.4; alveolar length of upper molariform teeth, 30.4. _Comparisons._--From topotypes and near topotypes of _Castor canadensis taylori_, _C. c. pallidus_ differs as follows: Size smaller; tail and hind foot shorter. Color: Markedly lighter throughout. Skull: Nasals shorter and wider (breadth of nasals averages 54 per cent of length of nasals, as opposed to 46 per cent); nasals barely projecting posteriorly beyond premaxillae; rostrum shorter; zygomatic breadth relative to basilar length less; mastoid breadth actually as well as relatively greater; interorbital breadth greater; occipitonasal length shorter rather than longer than condylobasal length; tympanic bullae smaller; coronoid process higher and wider; cheek teeth narrower. From specimens of _Castor canadensis baileyi_, from 20 miles north northeast of Elko, Elko County, Nevada, _C. c. pallidus_ differs as follows: Body smaller; tail longer; hind foot shorter; ears shorter: Color: Markedly lighter throughout. Skull: Larger; nasals shorter and wider (breadth of nasals averages 54 per cent of length of nasals as opposed to 41 per cent); nasals barely projecting posteriorly beyond premaxillae; rostrum broader; zygomatic breadth relative to basilar length less; mastoid breadth actually as well as relatively greater; occipitonasal length less rather than greater than condylobasal length; tympanic bullae smaller; coronoid process higher and wider; cheek teeth narrower.