1917] Holden: Osteological Relationships of Beavers 95 
ASTRAGALUS 
On the medial side of the body of the astragalus is a tuberosity 
which is developed to a greater degree in the three subspecies of 
Castor canadensis than in Castor subauratus or Castor fiber. The 
groove on the medioposterior edge extends farther laterad in the three 
forms of canadensis than it does in subauratus. The lateral border 
of the head of the astragalus is twisted upward more in subauratus 
than in the three subspecies of canadensis or fiber. The median artic- 
ulating face for the caleaneum is broader posteriorly in belugae, fiber, 
and phaeus than it is in leucodonta or subauratus. 
Number of differences noted between Castor subauratus and Castor 
canadensis, four. Castor fiber conforms with swbauratus in two, and 
with canadensis in two. 
CaLCANEUM 
In the three subspecies of Castor canadensis there is a well-defined 
medial tuberosity which is lacking in Castor subawratus and Castor 
fiber. In the three forms of canadensis and in fiber the median and 
anterior articulating faces make an angle anteriorly of about forty- 
five degrees with the axis of the caleaneum, while in subawratus they 
make an angle of about thirty degrees. There is a decided tendency 
for the sustentaculum of swbauratus to be more rounded mediad than 
it is in the three subspecies of canadensis. 
The plantar surface of the caleaneum in the three forms of cana- 
densis and in fiber is wider and more uniform in width for its entire 
length than it is in swbauratus, where there is a tendency for it to 
have a constriction directly below the sustentaculum. 
On the distal margin of the lateral face of the body is a process 
which is more highly developed in canadensis than in subauratus or 
fiber. As viewed from the plantar surface, the body of the caleaneum 
is less curved in subauratus and fiber than it is In canadensis. 
Number of differences noted between Castor subauratus and Castor 
canadensis, seven. Castor fiber conforms with suwbauratus in three, 
and with canadensis in three. 
Total number of differences noted between Castor subauratus and 
Castor canadensis, 156. Castor fiber conforms with subawratus in 
eighty-nine (58 per cent); with canadensis in fifty-three (33 per 
cent) ; and fourteen (9 per cent) are not clearly subject to assignment. 
