742 DR. J. E. GRAY ON STELLER's SEA-BEAR. [June 18, 



and lower surfaces of the middle-aged Japanese and of the very young 

 Californian skulls (see figs. 2, 3, 4, 5, pp. 738-741), confirmed by 

 Mr. Allen's figures of the North-Pacific species. Hitherto the posi- 

 tion of the teeth compared with other parts of the skull has been 

 considered very little liable to vary. Indeed, in all the known species, 

 it has been supposed that the teeth after the first change, which 

 occurs a very short time after birth, retain their relative position 

 during the whole of their life. This has been proved by the exami- 

 nation of skulls of different species and ages ; and the chief difference 

 between the two skulls in the British Museum from Monterey and 

 Japan (?) is that the adult Monterey skull is very heavy, and very 

 much wider (that is to say, that the width between the zygomatic 

 arches is the same as the length from the front upper cutting-teeth 

 to the tubercle on the hinder part of the edge of the hinder nasal 

 opening), the palate has much greater width and is rather contracted 

 behind, and there is a very great space between the fourth and fifth 

 upper grinders. The hinder grinder has a small crown and a large 

 base, consisting of two very distinct roots, the front of which is much 

 the largest. The grinders are much more cylindrical and have more 

 regularly conical crowns than the younger specimen. 



The lower jaw is very strong and heavy, rather abruptly truncated 

 in front, and is as high under the fifth as under the first grinder ; 

 that is to say, it is not dilated in front, but the same height the whole 

 length. (See P. Z. S. 1859, pi. 72.) 



The younger skull said to have come from Japan (figs. 2, 3) is much 

 longer and narrower, and is peculiar for having two very large occipital 

 condyles, which are as wide as half the width of the skull at the con- 

 dyles of the lower jaw, very unlike the size of the condyles in the two 

 nearly adult jaws figured by Mr. Allen ; unfortunately this part is 

 deficient in the adult skull from Monterey in the British Museum. 

 The skull is light and thin, and the sutures are still visible. The width 

 at the condyles of the lower jaw is considerably less than the length 

 from the front cutting-teeth to the tubercles on the side of the hinder 

 nasal opening. The grinders have elongated conical rather com- 

 pressed crowns, and a distinct basal collaret ; the fifth hinder one is 

 more compressed, and only separated from the fourth by a space 

 about as wide as the fifth tooth. This tooth has a compressed and 

 very indistinctly divided base, very unlike the two diverging and un- 

 equal lobes of the adult skull. The lower jaw is much dilated in 

 front, and very obliquely truncated and swollen, having a very 

 different appearance from that of the adult animal. The grinders 

 are rather elongate-conical, without any or only a slight lobe on the 

 front of the collaret, the fifth or hinder grinder, with a smaller 

 more compressed crown, having a lobe on the front and hinder edge. 

 The canines are large, rather compressed, with a sharp cutting-edge 

 on the hinder side ; the outer upper cutting-teeth are large, nearly 

 half the size of the canines ; the crown of the grinders is elongate- 

 conical, all these parts being much more acute and compressed than 

 in the adult skull, the teeth becoming thicker and more cylindrical 

 by age. 



