DIFFERENTIAL CHARACTERS. 



157 



ences I venture to predicate tlie existence of two species, using- 

 the term " species " in its commonly accepted sense. To show 

 more readily what these differences are, I present herewith a 

 series of figures of skulls of both old and young of the two 

 forms. The skulls selected for this purpose are average exam- 

 ples of a considerable series, the adult skulls being those of 

 males of strictly comparable ages. 



Fig. 15. Odobcenus rosmarus. 



The skulls of the two species seen in profile (Figs. 14 and 15) 

 exhibit the following differences : The first and most obvious 



