32 
JOUKNAL OF MAMMALOGY 
different seasons of the year, the specimens available at present are 
sufficient to show reliable characters. A much more extended study 
will be necessary to determine the limits of range of this form and 
whether it conforms strictly to the drainage system of the Missouri 
River or only a part of it. The form may be known by the following 
description : 
Castor canadensis missouriensis subsp. nov. 
Type from Apple Creek, 7 miles east of Bismarck, North Dakota. Male, 
immature. No. 205763, U. S. National Museum, Biological Survey Collection. 
Collected September 1, 1914, by Vernon Bailey. Original No. 9,703. 
General characters: — Slightly smaller than canadensis and much paler and duller 
brown. Skull more triangular in outline, not so massive and heavy; much like 
that of mexicanus, shorter and heavier than that of frondator. From mexicanus 
the colors differ in being noticeably duller and darker; hom. frondator , duller, 
and not so rusty. 
Color of type specimen in fresh short September fur, back from nose to tail, 
rich hazel brown; duller on sides, and more yellowish on sides of face and neck; 
lowerparts smoky grayish brown, with a touch of light chestnut at base of tail 
and over tops of feet. Young of year almost exactly the same in coloration. 
Specimens from the Yellowstone Park (Yanceys), in long winter fur, are slightly 
brighter hazel over the back, but very similar otherwise. 
Skull of type specimen not sufficiently developed for fair comparison with 
old individuals, but agreeing in general characters with adults from the same 
region. A fully adult skull in the National Museum Collection, No. 2377, labeled 
“Upper Missouri, Lieutenant Warren,” and another good skull from old Fort 
Stevenson (McLean County), also show the triangular shape, light structure, and 
narrow interorbital region of this form. 
Measurements of type in the flesh (probably 18 months old and not fully 
grown) — Total length, 900; tail, 270; hind foot, 170; naked part of tail, length, 
230, width, 130 mm. Skull, basal length, 110; nasals, 41 (22.4 wide); zygomatic 
width, 87; mastoid width, 60; interorbital width, 21; postorbital width of brain 
case, 45; alveolar length of upper molar series, 27.5 mm. Measurements of 
skull No. 2377, U. S. National Museum Collection, from Upper Missouri, basal 
length, 130; nasals, 49; zygomatic width, 102; mastoid width, 67; interorbital 
width, 25; postorbital width of brain case, 48 alveolar length of upper molar 
series, 32 mm. Weight of type specimen estimated at 35 or 40 pounds. 
