76 University of California Publications in Zoology [Vou. 17 
gy 
INTRODUCTION 
ScoPr 
The following paper contains the results of a detailed comparison 
of certain extra-cranial parts of the skeletons of Castor subauratus, 
Castor canadensis, and Castor fiber. This study was originally under- 
taken with the first two species, to determine whether the osteological 
data which could thus be obtained would confirm the systematic status 
of the forms as indicated by the study of the skins and skulls alone 
(see Taylor, 1916). After these observations had been recorded, a 
single skeleton of Castor fiber was obtained and the condition of each 
point of variance between canadensis and subauratus was noted. 
These results, also, have been incorporated. 
The specific characters of canadensis, as regards the skeletal parts 
studied, have been taken from the three subspecies Castor canadensis 
belugae, C. c. lewcodonta, and C. c. phaeus. In addition to the com- 
parisons given in the text of the present paper, a tabulated statement 
is added, giving the most obvious differences to be noted in the bones 
of the limbs and of the pectoral and pelvie girdles. 
It should be remembered that the comparisons, throughout, are 
based upon a small series of skeletons, so that the examination of 
further material may prove that some of the characters given are not 
diagnostic. So far as it has been found feasible, all characters which 
appear to be of average persistence, but which fail in one or two in- 
stances in the series studied, have been noted as ‘‘tendencies.”’ 
MATERIAL 
The major portion of the observations herein contained were made 
from the following specimens now in the California Museum of Verte- 
brate Zoology. 
No. 
Castor canadensis phaeus 210 
Sex Locality 
3S  Hasselborg Lake, Admiralty Island, 
Alaska 
Castor canadensis belugae 4347 ¢ Snug Harbor, Alaska Peninsula, 
Alaska 
Castor canadensis leucodonta 12101 @ Alberni, Vancouver Island, B. C. 
Castor subauratus 8869 ¢ San Joaquin River, near Grayson, 
Stanislaus Co., California 
2 San Joaquin River, near Grayson, 
Stanislaus Co., California 
Castor subauratus 8987 
