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 fully 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 fossa? are also quite different, 

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

 and broader in the Atlantic AYalrus. 



FIG. 27. Odobcenuis 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, the skull in the latter being heavily developed 

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

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



