STRUCTURE OF HOOKEE'S SEA-LION. 379 



of this paper. I there took pains to point out that, from certain external characters 

 afforded by the nose and ears, the Sea-Lions already known to us could be very distinctly 

 separated into two groups. 



Again, the visceral anatomy of the Otariidse, although known within very narrow 

 limits, affords grounds for specially uniting together certain forms, and separating these 

 from others. 



So far as they go, all these characters — external, visceral, and osteological — point 

 the same way, and tend to divide the Otariidse into two divisions : the one comprises 

 only Otaria jubata ; the other will contain all the rest of the known forms. This 

 distinction will be best emphasized by applying separate generic names to the two 

 divisions ; I am, however, quite of opinion that it is, in many respects, not advisable 

 to separate so well-marked a group as are the Sea-Lions into two genera. As for the 

 numerous genera which Dr. Gray and Prof. Peters have from time to time proposed, 

 most of them appear to me to be quite unnecessary. These two genera should be 

 Otaria and Arctocephalus, and they will be defined as follows : — 



Otaria. Arctocephalus. 



Nose broad and truncated. Nose narrow and pointed. 



Ears short. Ears relatively long. 



Palate deeply hollowed out and truncated Palate not excavated nor truncated poste- 



posteriorly. riorly. 



Pterygoids without a hook-like process. Pterygoids with a recurved process. 



Posterior margin of nasals on a level with Posterior margin o£ nasals behind zygoma 



zygoma and suborbital process. and suborbital process. 



On the whole, the osteological characters which separate the two genera are more 

 specialized in Otaria than in Arctocephalus ; that is to say, the young skulls of Otaria 

 are more like the adult Arctocephalus than the young skulls of Arctocephalus are like 

 the adult skulls of Otaria. 



The genus Otaria will have to be limited to the species Otaria jubata, for it may be 

 now, I think, asserted with safety that the following species — viz., 0. minor, Gray, 

 O.pygmcea, Gray, 0. byronia, Gray, 0. leonina, Gray, O.godeffroyi, Gray, and 0. ulloce, 

 Peters — are synonyms of 0. jubata. Arctocephalus will contain all the remaining Sea- 

 Lions. I had at first intended to go into the question of the species of Otariidse in 

 connexion with the present communication ; this, however, proved to be impossible, 

 owing to the absence from our collection of representatives of a considerable number 

 of species or reputed species. 



It will be noticed that the conclusion to which the facts described in the present 

 paper lead, viz., that there are, at most, only two distinct genera of Sea-Lions ( Otaria and 

 Arctocephalus), is not a new one ; although some recent authors, such as Gray, Peters, 

 Gill, Allen, Burmeister, and others, have allowed a considerable number of genera, 



