DIFFERENTIAL CHARACTERS. 



165 



Another difference not yet noted consists in the greater 

 length and massiveness of the zygomata in the Pacific species, 

 in which they are fnlly one-third heavier than in the Atlantic 

 species; they being in the former both deeper and thicker. 

 (This is well shown in the above given figures of the skulls as 

 seen in profile and from above and below, but especially as 

 as seen from below.) The orbital fossae are also quite different, 

 they being relatively long and narrow in the Pacific, and shorter 

 and broader in the Atlantic Walrus. 



Fig. 27. Odobcenus obesus. 



To sum up in a word the above-detailed cranial differences 

 between the two species of Walruses, the skull of the Pacific 

 animal is heavily developed anteriorly and relatively much less 

 so posteriorly, while in the Atlantic Walrus just the reverse of 

 this obtains, tlie skull in the latter being heavily developed 

 jjosteriorly and relatively less so anteriorly. The axis of vari- 

 ation being at the posterior border of the orbital fossse, the 



