448 University of California Publications in Zoology [Vol.12 



XVIII. Measurements and Ratios of Scaled Portions of Tails 



All measurements in millimeters, and taken in dry skins; see fig. H, p. 431 



Ratio 



Museum width to 



Subspecies — number Length Width length 



Castor s. subauratus 16385 298 124 41.6 



Castor s. subauratus 16382 305 137 45.0 



Castor s. subauratus 16383 311 133 42.8 



Castor s. subauratus 8988 310 140 45.2 



Castor s. subauratus 12654 320 139 43.4 



Castor c. pacificus 126190 185 74 38.9 



Castor c. frondator 20751 232 113 48.9 



General cranial characters 



Crania compared. — Castor subauratus subauratus, nos. 16383 $ , 

 16384 S , 8988 9 , and 12654 5 , Mus. Vert. Zool., all from the vicinity 

 of Grayson, San Joaquin River, Stanislaus County, California ; Castor 

 canadensis pacificus, nos. 3672, 71276 9 , 71812 $ , 71814 9 , 

 87628 9 , 87629 3 , 126190 $ , U. S. Nat. Mus., all from the main- 

 land of Washington State ; Castor canadensis frondator, nos. 60354 

 S , 3594 S , 35946 9 , from the Colorado River, Mexico, 15 miles 

 south of Yuma, Arizona, and from the San Pedro River, Mexico, 

 respectively. 



Comparable crania of Castor s. subauratus exhibit a tendency 

 to be larger than those of Castor c. pacificus. They exceed those 

 of pacificus absolutely in width of nasals and ratio of width of 

 nasals to basilar length. Vertical diameter of foramen magnum 

 less in all comparable crania of subauratus than in pacificus or in 

 frondator with one exception {pacificus no. 71276 has this diameter 

 11.2, which is the same as that in subauratus no. 16383) ; and 

 associated with this difference, the ratio of vertical diameter of 

 foramen magnum to basilar length is less in the comparable crania 

 of subauratus than it is in pacificus (with the single exception men- 

 tioned) or in frondator. 



The anterior dilation of the nasal outline in subauratus is 

 marked; it clearly separates the California form from pacificus, 

 but not from frondator, though absolute measurements in subaura- 

 tus exceed those in the latter. 



In subauratus the extension of the nasals posteriorly of a line 

 connecting the points of the antorbital processes is greater than in 

 pacificus, but less than in frondator (actual measurements: sub- 

 auratus, no. 16383, 1.0 mm.; 8988, 0.8. In pacificus, nasals pos- 



