2ou 



THE AMERICAN NATURALIST [Vol. XLIX 



ti-aquatic), non 



hemisphei 

 tions; f< 

 modified £ 



fins or flippers ; denti- 

 aodified tubereulo-sec- 

 the posterior upper 



trenchant and crushing type, the 

 last upper premolar and first lower 

 molar strongly differentiated as 

 carnassials, the former 3-rooted, 

 its inner lobe in front of middle 



posterior to level of anteorbital 

 foramen, at point of greatest me- 

 chanical pfiicieney; auditory bulla 

 moderately or considerably in- 



n ; presence 



s by w 

 family 



verged as terrestrial i 



nd deep (depth of 



Chiefly characters of propor- 



the teeth. Characters clearly mani- 

 fested in lower and middle Eocene 

 time and taking on their modern 

 aspect in early Oligocene time. 



teeth heavy and large, the length 

 of carnassial and upper molars 

 together contained about 2V 2 times 



