432 University of California Publications in Zoology [Vol. 12 



Comparable skins of the two subspecies are distinguishable as 

 follows: the single skin of belugae with both overhair and underfill- 

 thicker than in leucodonta; belugae paler in coloration than average 

 of leucodonta, particularly about base of tail, which is near cinna- 

 nion-buff in belugae, varying from near hair brown to a shade 

 between chocolate and bay in leucodonta; tails are similar in gen- 

 eral outline. 



Comparison With Castor canadensis canadensis Kuhl 



Skulls of belugae comparable with canadensis as regards age 

 have outline of nasals different ; maxillary tooth-row longer in com- 

 parable crania; ratio of the maxillary tooth-row to basilar length 

 averaging greater. Belugae, according to the table of measurements, 

 has teeth tending to be broader and longer than in canadensis. A 

 detailed comparison of external characters of the Cook Inlet race and 

 canadensis will be found in table VII, opposite. 



The following table illustrates differences in tail outline : 



VI. Measurements and Ratios of Scaled Portions of Tails 

 All measurements in millimeters, and taken from dry skins 



Subspecies — 

 Castor canadensis belugae 

 Castor canadensis canadensis 

 Castor canadensis canadensis 

 Castor canadensis canadensis 



The tails of 4347 and 4358 were considerably crinkled and dried 

 hard, so that their measurements are less dependable than those of 

 the others. 



Comparison with Castor canadensis phaeus Hfller 



Separated from Castor canadensis phaeus Heller, inhabiting 

 Admiralty and probably neighboring Alaskan islands, on following 

 characters : belugae with broader interorbital constriction than in 

 phaeus; nasals of different outline, these bones not tapering caudad 

 as they do in phaeus; nasals with lesser degree of extension back 

 of a line joining the points of the antorbital tubercles. While indi- 

 vidual specimens show intergradation in one or two of these char- 

 acters, as might be anticipated, it is true that in the series at hand 

 every specimen is clearly separable. Externally belugae is dis- 



