1917] Holden: Osteological Relationships of Beavers 85 
species of canadensis these edges form one continuous are (text-figs. 
M, N, 0). In fiber these edges, on the first two lumbar vertebrae, 
form an angle; but on the remaining vertebrae these edges are uneven. 
In the lumbar vertebrae of swhauratus and fiber there are one or two 
well-developed foramina on the ventral surface of the centra, while in 
the three forms of canadensis these foramina appear only on the last 
or the next to the last vertebra. 
In the series of swbauratus the anapophyses, which occur on the 
first, second, and even the third lumbar vertebrae, have a tendency 
to form an articulating surface with the metapophyses following (text- 
figs. M, N, O) ; in fiber and in the three subspecies of canadensis these 
processes do not articulate with each other. 
Fig. P.—Caudal view of second lumbar vertebra of Castor fiber, no. 19229. 
xX %. 
Fig. @.—Caudal view of second lumbar vertebra of Castor subauwratus, no. 
16385. X %. 
Fig. R.—Caudal view of second lumbar vertebra of Castor canadensis belugae, 
no. 4347. X %. 
Although the prezygapoplhyses of the third and the next to the last 
lumbar vertebrae extend laterally to a greater degree in subauratus 
and fiber than in the three subspecies of canadensis, the postzyga- 
pophyses of the same vertebrae extend laterally to a greater degree 
in phaeus than they do in belugae, subauratus, or leucodonta, while 
fiber exceeds even phaeus in this measurement. 
The prezygapophyses of the last lambar vertebra of phaeus spread 
laterally to a greater degree than do the same processes of subauratus, 
which in turn exceed those of belugae and leucodonta. 
Number of differences noted between Castor subauratus and Castor 
canadensis, thirty-six. Castor fiber conforms with subauratus in 
twenty-one of these, and with canadensis in thirteen; two are un- 
assigned. 
