MUSEUM OF COMPARATIVE ZOOLOGY. 35 



The form and position of the molars in the same species is also far 

 too variable to be of much taxonomic value, even in respect to genera,* 

 although they form one of the principal elements on which has been 

 based one of the latest generic revisions of the group.f 



The roots of the molars often vary considerably in the two sides of 

 the jaw in the same specimen, and most markedly in different co- 

 specific specimens of the same sex and age. In one of the males of C. 



* The details of the individual variation shown in numerous points by my specimens 

 of the North Pacific species will be more fully given later. 



t In October, 1869, Dr. J. E. Gray published the following classification of the Ola- 

 riadce, based, as will be seen, on a few eminently variable characters of the skull and 

 teeth. That it should have been otherwise than palpably unnatural and arbitrary could 

 hardly be expected. The alleged differences between the genera are very slight, and 

 in some cases almost inappreciable, as for instance between Zalophus and Neophoca; 

 the really important differences which sometimes exist between the different groups 

 being unmentioned. 



" Section I. Palate produced behind to a line even with the condyles of the jaws. Grind- 

 ers A — 6 Sea Lions. 

 Tribe 1. Otariixa. 



1. Otaria. East and west coast of .South America. 



Section II. Palate only extended behiivl to a line even with the middle part of the zygomatic 

 arch. Sea Beaks. 

 Tribe 2. Callokiiinixa. Grinders 4~4 ; skull oblong; face broad, shorter than 

 the orbit ; forehead arched. 



2. Callorhinus. Northwest coast of America. 



Tribe 3. Arctocephali.na. Grinders £ — | ; face of the skull shelving in front; 

 the fifth and sixth grinders behind the front of the zygomatic arch. 



3. Phocaixtos. Grinders large, lobed, the six upper with two notches ou their 



hinder edge. South America. 



4. Arctocephalus. Grinders thick; crown conical. Africa. 



5. Euolaria. Grinders large, subcylindrical; crown conical; fiice broad. South 



America. 



6. Gypsophoca. Grinders moderate-sized, compressed, with a small, more or 



less distinct lobe on the front edge of the cingulum; face narrow, com- 

 pressed. Australia. 

 Tribe 4. Zalophina. Grinders 4 —1 large, thick, in a close, continuous series; 

 the fifth upper in front of the back edge of the zygomatic arch. 



7. ZaUphus. Grinders large and thick, in a close uniform series. South 



America. [ ! ] 



8. Neophoca. Grinders krge, thick, all equal, in a continuous uniform series. 



Australia. 

 Tribe 5. Eumetopiina. Grinders s — 4, more or less far apart; the hinder upper 

 behind the hinder edge of the zygomatic arch, and separated from the 

 other grinders by a concave space. 



9. Eumetopias. West coast of America. 



10. Arctophoca. West coast of South America." 



