1916] Taylor: Beavers of Western North America 439 



Specimens nos. 4347 and 210 are similar in coloration, the 

 former being slightly paler. No. 209 is much darker than either, 

 the rest of the series from Admiralty being nearest 209. 



XI. Measurements and Ratios of Scaled Portions of Tails 



All measurements in millimeters, and taken in dry skins 



Ratio 

 Museum width to 



Subspecies — number Length Width length 



Castor canadensis phaeus 209 240 130 54.1 



Castor canadensis phaeus 210 248 132 53.2 



Castor canadensis belugae 4347 245 115 47.0 



General cranial characters. — Crania compared: Castor canadensis 

 belugae, nos. 4219-4233, 4347, Mus. Vert. Zool., all from the Cook 

 Inlet region, Alaska ; Castor canadensis phaeus, nos. 209 S , 210 S , 

 Mus. Vert. Zool., from Admiralty Island. Specimens 209 and 210 

 from Admiralty Island, and specimens 4220, 4225 and 4347 from 

 Cook Inlet comparable as to age. 



Skulls of phaeus slightly smaller than the average of those of 

 belugae. Interorbital constriction narrower in phaeus than in 

 eighteen of the twenty-two specimens of belugae of all ages figured. 

 Nasals longer, more tapering posteriorly. Sharp process medially 

 in interpterygoid fossa reduced in phaeus. Foramen magnum 

 averaging broader in phaeus. Vertical diameter of foramen mag- 

 num in no. 209 exceeding that in any specimen from Cook Inlet, 

 but itself exceeded by no. 77150 from Stuart Lake, British Colum- 

 bia. Teeth narrower in phaeus. proportionally to their length. 

 Maxillary tooth-row averaging longer, consequently ratio of max- 

 illary tooth-row to basilar length greater in phaeus. No. 4233, the 

 youngest cranium from Cook Inlet, furnishes the single exception 

 to this rule. In this specimen the ratio of maxillary tooth-row to 

 basilar length is greater than in no. 210. Coronoid process of 

 mandible lighter in phaeus. Lateral ridge on rostrum larger in 

 phaeus. Hamular blades (see fig. P, p. 430) broader (no. 210, 4.1 

 mm.; 209, 4.1. No. 4347, 2.5; 4225, 2.5; 4224, 3.1). Distance from 

 most dorsal point on outline of foramen magnum to inion less 

 (see fig. G, p. 431 ; no. 210, 19.4 mm. ; 209, 17.1. No. 4347, 20.5 mm. ; 

 4225, 22.4; 4224, 22.7). 



