1917] Holden: Osteological Relationships of Beavers 59 
lateral portion of the spine in subauratus and fiber has a projecting 
edge on its glenoid side, which extends from the acromion about two- 
thirds of the way to the suprascapular border; in the three subspecies 
of canadensis this projecting edge is shorter, ending where the spine 
twists ventrad. 
The angle formed by the glenoid border and the coracoid border, 
if produced, is greater in subauratus than in fiber or in the three 
forms of canadensis, or, it might be said, these borders approach each 
other more rapidly in swbauratus. Fiber and the three forms of cana- 
densis have a more nearly sharp-cornered superior angle than has 
subauratus (pl. 7). The coracoid process of subauratus and _ fiber 
has a much sharper point than it has in the other three forms, but 
it is heavier in canadensis and fiber. The ventral extremity of the 
acromion tends to be more nearly styliform and narrower in the three 
subspecies of canadensis than in subauratus or in fiber. 
Number of differences noted between Castor subauratus and Cas- 
tor canadensis, twelve. Fiber conforms with subawratus in seven; 
with canadensis in four; and one is indeterminate. 
CLAVICLE 
The shaft of the clavicle in Castor subauratus, if projected upon 
the dorsoventral and cephalocaudal planes, would describe ares, the 
center on the first of which would be located mediodorsad, and that 
of the second, laterocephalad (pl. 8, figs. 30 to 37). In the three forms 
of Castor canadensis and in Castor fiber the shaft is straight. On the 
costal surface, near the dorsal edge and about one centimeter from 
the acromial extremity, there is a small fossa, evidently for the attach- 
ment of muscle; this is deeper in subauratus and fiber than in the 
other forms. 
Number of differences noted between Castor subauratus and Castor 
canadensis, three. Fiber conforms with suwbauratus in one, and with 
canadensis in two. 
Humerus 
The base of the epiphysis of the greater tuberosity is broader in its 
anteroposterior dimension in Castor fiber and in the three subspecies 
of Castor canadensis than in Castor subauratus. The bicipital groove 
is longer and deeper in fiber and in the three forms of canadensis 
than it is in subauratus (pl. 9). The olecranon fossa is more clearly 
