lee) 
University of California Publications in Zoology  {Vou.17 
As a rule, the transverse processes which extend farthest laterally 
are borne on the first caudal vertebra in canadensis; in subauratus on 
the fourth; and in fiber on the second. 
Number of differences noted between Castor subawratus and Castor 
canadensis, eleven. Fiber conforms with subauratus in three; with 
canadensis in four; and four are indeterminate. 
Riss AND STERNUM 
There is a tendency for the first six ribs in the three subspecies of 
Castor canadensis and in Castor fiber to be flattened upon the trans- 
verse axis to a greater degree than are the ribs of subawratus. 
Owen (1866, p. 364) gives the number of ribs in Castor as fifteen 
pairs. This is the number found in subauratus, but not in fiber or 
in the three subspecies of canadensis, which have fourteen. There are, 
however, only seven pairs of true ribs in swbawratus and the three 
subspecies of canadensis; while Owen (1866, p. 366) gives the number 
in Castor as eight. Morgan (1868, p. 52), who was deseribing cana- 
densis, records seven pairs of true ribs. 
The sternum of swbauratus and fiber is broader and thicker than 
is the sternum in the three forms of canadensis. 
Number of differences noted between Castor subauratus and Cas- 
tor canadensis, four. Fiber conforms with subauratus in two of these 
and with canadensis in two. 
ScAPULA 
The suprascapular border tends to be straighter in swbauratus 
and fiber than in the three subspecies of canadensis (pl. 7). In the 
last named forms the vertebral margin (BNA) follows the are of a 
circle with its center located near the glenoid border, while in swb- 
auratus and fiber the center of the are of this border is located near 
the spine (pl. 7). The glenoid border is thicker in swbauratus than 
in the three forms of canadensis. 
The spine tends to originate at its dorsal extremity closer to the 
coracoid border in fiber and in the three forms of canadensis than 
it does in subauratus (pl. 7). About half-way between the acromion 
and the suprascapular border there is a decided ventral twist to the 
lateral portion of the spine in the three forms of canadensis, while the 
spine of swhauratus and fiber is comparatively straight (pl. 7). The 
