158 



ODOB^NUS OBESUS PACIFIC WALRUS. 



is perhaps that presented by the tusks, which, in the Pacific 

 species (Fig. 14), are much longer and thicker than in the other 



(Fig. 15), less incurved and 

 more convergent; their alve- 

 oli are deeper and thicker, 

 with heavier walls, thereby 

 giving much greater fullness 

 to the front wall of the skull, 

 I even modifying the form of 

 | the nasal bones. The front 

 outline, as seen in profile, is 

 very oblique in the Atlantic 

 species, while in the Pacific 

 species it is nearly vertical, 

 the front edge of the nasal 

 bones being very little poste- 

 rior to the front border of the 

 base of the tusk, while in the 

 Atlantic species they scarcely 



FIG. 16. OdobivHu* ru*>nrus. pass beyond a vertical line 



drawn from the hinder border of the tusk. The orbits in the 



Pacific species are 

 placed more ante- 

 riorly than in the 

 other. 



In the front view 

 of the skulls, the 

 muzzle is seen to be 

 much smaller in the 

 Atlantic species 

 (Fig. 16) than in the 

 Pacific (Fig. 17), 

 with, however, not 

 very marked differ- 

 ences in outlines and 

 proportions. The 

 receding upper bor- 

 der in the latter is a 

 marked feature. 

 The difference in 

 size here shown is 

 FIG. i7.0dol(enus obcsus. an important one, 



since the two skulls compared differ very little in general size, 



