XIX. COMPARISON OF CRANIAL CHARACTERS OF Castor subauratus subauratus TAYLOR, FROM THE SAN JOAQUIN VALLEY CALIFORNIA with „ ♦ 



pacificus RHOADS. FROM WASHINGTON STATE, AND WITH Castor canadensis frondator MEARNS, FROM COLORADO AN D SAN PEDRO RIVERS MEXKO """' 



Castor subauratus subauratus 



Points of Comparison (nine examples) 



Median constriction of interparietal Not so much constricted on the average as 



in pacificus. 



Hamular processes of pterygoid bones Thicker and heavier than in either sub- 

 species. 



Ventral contour of hamulars Straightest. 



Median process in interpterygoid fossa Heavy and blunt. 



Auditory bullae Little inflated. 



Lateral ridge on auditory bullae Strongly developed. 



Paroccipital process More prominent than in the other sub- 

 species, extending more posteriorly, flat- 

 tened instead of knob-like. 



Relation of condylar foramina to occipital 

 condyles Condyles more pulled out posteriorly; fora- 

 mina in plain view on basi-cranial aspect 

 of skull in most specimens. 



Castor canadensis pacificus 



(seven examples) 



More constricted, on the average, than in 



subauratus. 

 Lighter than in subauratus. 



Not so straight as in subauratus. 

 Light and sharp (that of no. 71812 ap- 

 proaching a blunt condition). 

 Comparatively much inflated. 



Weakly developed. 



Not so prominent as in subauratus, extend- 

 ing more ventrally, less flattened, more 

 knob-like. 



Intermediate in condition between subau- 

 ratus and frondator. 



Castor canadensis frondator 

 (two examples) 

 Practically intermediate in degree of con- 

 striction. 

 Lighter than in subauratus. 



Not so straight as in subauratus. 

 Light and sharp. 



Intermediate in condition between subau- 

 ratus and pacificus, though nearer the 

 latter. 



Intermediate in condition between subau- 

 ratus and pacificus, though nearer the 

 latter. 



Not so prominent as in subauratus, extend- 

 ing more ventrally, less flattened, more 

 knob-like. 



Condyles more folded anteriorly; foramina 

 not in plain view on basi-cranial aspect 

 of skull, as in most examples of subau- 

 ratus. 



