162 



ODOBJENUS OBESUS PACIFIC WALRUS. 



resented. The young skulls here compared are of nearly the 

 same age ; but unfortunately the absence of the occipital por- 

 tion of the skull in the only Pacific specimen of this age (Fig. 

 22) I am able to figure renders it impossible to compare by fig- 

 ures the occipital region in young specimens. Other specimens 



FlG. 22. Odobtenus olesus. 



FIG. 23. Odobwnns rosmarus. 



young enough to have the sutures still open show the differ- 

 ences seen in the occipital region of older skulls. 



Another difference, but one apparently less constant than the 

 others, is the presence in the young skull of the Pacific "Walrus 

 (Figs. 22 and 24) of an extension posteriorly of the interinaxilla- 

 ries for two-thirds of the length of the nasals. In the Atlantic 

 skull (Figs. 23 and 25), the interrnaxillaries do not enter into the 

 dorsal outline of the skull, but terminate at the anterior bor- 

 der of the nasals. This difference is open to exceptions, and is 

 not offered as a character of importance, since the same modifi- 

 cation or backward prolongation of the intermaxillaries occurs 

 occasionally in the Atlantic species, and is sometimes absent in 

 the Pacific species, while in some examples the intermaxillaries 

 reach the dorsal surface only as isolated ossicles between the 

 nasals and maxillaries. As a rule, however, the conditions in 

 this respect shown in the young skulls here figured appear to 

 be diagnostic of the two species. 



