186 MAMMALIAN DENTITION 



l|, C j, P-|, My. total 34. 



The third upper incisor is caniniform, each of the others 

 shows a well-marked notch on the crown someAvhat similar to 

 that observed in terrestrial Carnivora. The lower incisors are 

 slightly procumbent. The canines are stout and slightly com- 

 pressed, the upper ones vertical, the lowers directed somewhat 

 outward. The premolars and molar of the maxilla are sec- 

 ondarily simple teeth each with a well-marked cingulum sur- 

 rounding the base of the crown. Their single cusp probably 



Fig. 66. — Lateral view of skull of Gillespie's Sea-lion (Zalophus californianus, 9.7451-1). 

 Note the secondary reversion of the cheek teeth to conical form. 



represents the paracolic The mandibular cheek teeth are also 

 simple but the basal cingulum rises into a small cusp in front 

 and behind the apex of the tooth which may be the homologue 

 of the protoconid. 



The Seals differ quite considerably according to species in 

 the number of their incisors and their cheek teeth show vary- 

 ing degrees of reduction to a simple or a secondarily tricono- 

 dont form. The fact that great variation occurs even among 

 individuals indicates that this family is even now evolving at 

 a rapid rate. 



The Walrus, Odobenus rosmarus, is a gigantic animal living 



