168 University of California Publications in Zoology [Vol. 10 



Color. — Similar to Castor canadensis frondator but darker. 

 The hair dorsally is much the same in coloration, which is hazel 

 td clay color of Ridgway's Nomenclature of Colors (1886). The 

 underfur is in subauratus nearer chocolate than seal brown, while 

 in frondator it approximates Prout brown. Ventral underfur in 

 subauratus sepia, in frondator gray, varying about drab gray, 

 iM-i-ii drab and drab. 



Castor subauratus possesses a golden sheen dorsally and ven- 

 trally, which is nearly lacking in leucodontus. Hair ventrally 

 in the new species varies about buff (ochraceous-buff to pinkish 

 buff), while in leucodontus it is chestnut. Coloration of the 

 area about the base of the tail not so deep in subauratus as in 

 It ucodontus. 



Castor subauratus has less hair than lias Castor c. leucodontus, 

 but more than Castor c. frondator. 



Skull. — There are many differences between the skulls of 

 Castor subauratus, Castor c. leucodontus, and Castor c. frondator, 

 the most important of which are the form of the nasals, which 

 are more expanded in subauratus than they are in either of the 

 other two subspecies; and the shape of the foramen magnum, 

 which is proportionally very wide as compared with its height 

 in the California species, much more so than in the two sub- 

 species with which it is here compared. The ratio of the width 

 of nasals to basilar length is 22.4 per cent in the type of 

 subauratus (no. 12tir>4. Mus. Vert. Zool.) ; in leucodontus (no. 

 12107, Mus. Vert. Zool.) it is 19.8 per cent; while in frondator 

 (no. 60354, U. S. Nation. Mus.) it is 20.9 per cent. The ratio of 

 the vertical diameter of the foramen magnum to basilar length 

 is 8.0 per cent in the type of subauratus (no. 12654, Mus. Vert. 

 Zool.) ; in leucodontus (no. 12107, Mus. Vert. Zool.), it is 11.25 

 percent; while in frondator (no. 60354, U. S. Nation. Mus.) it is 

 12.4 per cent. 



Tail. — Proportions of tail separate Castor subauratus from 

 Castor c. frondator. Average ratio width of tail to length in 

 Castor subauratus is 42.42 per cent (extremes 37.6-45.2) ; in 

 frondator (no. 20751, U. S. Nation. Mus.) 49.1 per cent; in 

 leucodontus, 41.32 percent (extremes 31.8-51.0). 



