1917] Holden: Osteological Relationships of Beavers 99 
GENERAL OBSERVATIONS 
It has not been possible to formulate any one general statement 
covering the differences between the three species of Castor. The fact 
that swbauratus has one more thoracic-lumbar vertebra might signify 
that, in this character at least, swbauratus is the most primitive form. 
The three subspecies of canadensis are more closely related, inter 
se, than is subauratus or fiber to any one of them. Also it is to be seen 
that swbawratus and fiber are more closely related than fiber and cana- 
densis. The differences, however, between subauratus and fiber are so 
ereat as to preclude consideration of these two forms as conspecific. 
The relative similarity, however, brings forward many interesting 
questions, to which no attempt is here made to give answers. 
Transmitted August 4, 1916. 
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