424 Proceedings of the 



In the skull of the common seal {Calocephalus vitulinus), 

 which represents the inauriculatse, there is no post-orbital 

 process ; the mastoid can scarcely be called a process, and 

 seems to form a part of the large-rounded tympanic bulla. It 

 is separated from the bulla by a distinct groove, extending 

 from the stylomastoid foramen obliquely backwards and in- 

 wards. In the section to which the Calocephalus vitulinus 

 belongs there is no trace of an ali-sphenoid canal. In the 

 auriculatae there is a distinct post-orbital process and an 

 ali-sphenoid canal ; the mastoid process is largely developed, 

 and stands apart from the tympanic bulla, which is small and 

 projecting. The carotid canal has the same direction as in 

 the Canidss ; while in the common seal it enters farther for- 

 ward, and does not again appear externally. The orbito- 

 sphenoids are greatly compressed in front, so that the optic 

 foramina seem to have coalesced into one. These osteological 

 characters have afforded a basis for the division of the Pho- 

 cidse into three sub-families. 



1. Arctocephalina. — A post-orbital process ; a distinct ali- 

 sphenoid canal ; mastoid process strong and salient, its sur- 

 face continuous with the tympanic bulla. This sub-family 

 contains two genera, — Otaria and Arctocephalus. 



2. Trichecina. — No post-orbital process ; an ali-sphenoid 

 canal. One genus and one species only known, — Trichecus 

 Rosmarus (walrus). 



3. Phocina. — No post-orbital process; no ali-sphenoid canal ; 

 mastoid process swollen, and seeming to form part of the tym- 

 panic bulla. 



By examining this Californian skull, it will be seen that the 

 osteological characters correspond to those ascribed to the sub- 

 family Arctocephalina. There is a well-developed post-orbital 

 process, and a distinct ali-sphenoid canal. The mastoid is a 

 strong, irregular-shaped process, deeply impressed by the 

 muscles attached to this portion of the cranium. The carotid 

 canal commences directly in front of the foramen lacerum 

 jugulare, and again appears at the anterior part of the tym- 

 panic bulla. The foramen condyloideum is situated at the 

 posterior and inner margin of the foramen jugulare ; in the 

 common seal it is placed farther back, and directly behind the 



