of Sea-bears and Sea-lions. 25 



hollow, but become solid, and some rather thickened in old 

 age. The grinders of the second series, when they are first 

 developed in the very young animal, are rather crowded ; but 

 they soon become regularly placed, and they occupy the same 

 length in the margin of the jaw and the same situation relative 

 to the front edge of the zygoma and other parts of the jaw in 

 the young and the perfect animal ; so that the position of the 

 grinders in these parts affords a very good character for the 

 distinction of the species, and the dividing them into generic 

 groups. 



Zoologists who have not had the opportunity of examining 

 the skulls of the Sea-lions and Sea-bears seem to believe that 

 the teeth of these animals vary greatly in the form of their 

 crowns and their position relative to other parts of the jaw 

 during the age of the animal, and find a difficulty in making 

 out the characters of the species. 



The skulls, during their growth from youth to adult age, 

 chiefly lengthen between the back of the face and the brain- 

 case ; and the palate of the young is generally broad behind, 

 with a broad opening and a broad front margin to the internal 

 nostrils ; but as the skull ages, the back of the palate and the 

 opening to the internal nostrils gradually become narrower, 

 and the lobes on the hinder part of the side fold together over 

 the internal nostril. 



The lower edge of the lower jaws of the large skulls of old 

 Sea-lions, probably all males, is much spread out and ex- 

 panded. 



Judging by the very few specimens of the skulls of the very 

 young Sea-bears in the British Museum, and by the figures 

 of the skulls of the young that have been published, they 

 offer two variations in respect of the shape of the internal 

 nostrils : — 



In the first the opening of the internal nostril at the end of 

 the palate of the young, as of the adult animal, is short, broad, 

 truncated in front, with sometimes a central notch ; and the 

 edge of the internal nostril, in the very young animals, as in 

 Otaria, is near to the line between the condyles, but not so near 

 as in that genus ; and as the animal grows, and the bones of 

 the face lengthen, the opening of the internal nostril extends 

 further forward, and becomes gradually oblong, narrower, and 

 arched in front, as in Gypsophoca tropicalis, Phocarctos elon- 

 gatus, and Euotaria nigrescens. 



In the second, the hinder opening of the nostril of the 

 very young skull in CaUorkinus, as figured by Mr. Allen, in 

 Eumetopias Stelleri, as shown by the specimens in the Museum, 

 and. (judging by the half-grown specimens) in Ar otocephalus 



