1917 | Holden: Osteological Relationships of Beavers 93 
greater than in the forms of canadensis. The epiphysis of the great 
trochanter forms with the shaft an angle that, in subauratus and 
fiber, is nearer 90 degrees than it is in any of the three subspecies 
of canadensis (pl. 12). In the three last-mentioned forms and in 
fiber the intertrochanteric line is more clearly defined than in sub- 
auratus. The lesser trochanter in subauratus and fiber has a flattish 
epiphysis which faces proximad and mesiad, while in the three forms 
of canadensis the lesser trochanter ends in a moderately sharp point 
(pl. 12). Directly anterior to the lesser trochanter, on the mesial 
side of the shaft of the femur, is a fossa which is deeper in subauratus, 
fiber, and belugae than in leucodonta or phaeus. The third trochanter 
(see Owen, 1866, p. 381, for name) in the three forms of canadensis 
is less blunt at its lateral extremity than in swbauratus or fiber (pl. 12). 
Number of differences noted between Castor subauratus and Cas- 
tor canadensis, eight. Castor fiber conforms with subawratus in six, 
and with canadensis in two. 
TIBIA 
The tibia is longer in comparison with the length of the femur in 
the three subspecies of Castor canadensis than it is in Castor sub- 
auratus or Castor fiber. The difference between subauratus and 
phaeus, however, is slight, as will be seen from the following table: 
Ratio, 
Femur Tibia per cent 
(Ch Gy TOLNGNE TS eee eee 106.6 mm. 131.6 mm. 81.1 
C. e. belugae and leucodonta ............ 103.9 132.8 78.2 
C. subauratus (average of five) =) LOS:7 129.4 81.7 
(OL, LOVEI oo eee eee ere rere Serer ee ne eee ae 108.5 132.9 81.6 
Anterior to the anterior condyloid fossa there is a tuberosity 
which is much sharper in the three forms of canadensis than in swb- 
auratus or fiber. In all five forms of beaver the posterior face is 
deeply concave; but in swbauratus and fiber the condyloid fossa ends 
much less abruptly proximad than it does in the three forms of cana- 
densis. 
Subauratus and fiber have heavier interosseous crests than have 
the three subspecies of canadensis. The malleolar groove is also wider 
in subauratus and fiber than in the three forms of canadensis, but is 
deeper and longer in the three last-mentioned forms and in fiber. The 
posterior margin, or rim, of the malleolar groove is thinner in the 
three subspecies of canadensis than in subauratus or fiber. 
