PLATE 6 
Ventral view of the vertebrae from the sacral region; about one-half natural 
size. 
Fig. 9. No. 8987, Castor subauratus. 
Fig. 10. No. 12654, Castor subauratus 
Fig. 11. No. 12668, Castor subauratus. 
Fig. 12. No. 16385, Castor subauratus. 
Fig. 13. No. 19229, Castor fiber. 
Fig. 14. No. 210, Castor canadensis phaeus. 
Fig. 15. No. 4347, Castor canadensis belugae. 
Fig. 16. No. 12101, Castor canadensis leucodonta. 
Note that the centra of the first four vertebrae of fiber, belugae, and phaeus 
are fused, while in subauratus and leucodonta only three of the vertebrae are so 
joined (no. 16385 having only two). The lateral portions of the transverse 
processes of the third and fourth vertebrae can be seen to be thinner in cana- 
densis (and one specimen, no. 12654, of swbawratus) than in fiber or subauratus. 
The presence of the second rudimentary rib in fiber, and the tendeney for cana- 
densis to have a second rib to the ilium, can also be seen. 
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