423 Royal Society. 



Fam. PHOCID^. 



Molars all similar in structure. (The general characters need not 

 here be enumerated, being universally known.) 



Subfam. Arctocephalina. 



A postorbital process. An ali-sphenoid canal. 

 Mastoid process strong and salient, standing aloof from the audi- 

 tory bulla. 



Otaria. 



Arctocephalus. 



Subfam. Trichecina. 



No postorbital process. A distinct ali-sphenoid canal. 

 Mastoid process strong and salient, its surface continuous with 

 the auditory bulla. 

 Trichecus. 



Subfam. Phocina. 



No postorbital process. No ali-sphenoid canal. 

 Mastoid process swollen, and seeming to form part of the auditory 

 bulla. 



Morunga. Lobodon. 



Cystophora. Leptonyx. 



Halichserus. Stenorhynchus. 



Ommatophora. Phoca. 



ROYAL SOCIETY. 



Jan. 18, 1849. — "On the Development and Homologies of the 

 Carapace and Plastron of the Chelonian Reptiles." By Professor 

 Owen, F.R.S. 



The author commences by defining the several parts of which the 

 osseous thoracic-abdominal case of the Chelonian Reptiles is com- 

 posed, and briefly discusses the several opinions that have been 

 published with regard to their nature and homologies, dwelling 

 chiefly on that recently proposed by Prof. Rathke, in his work on 

 the Development of the Chelonian in which it is contended that the 

 carapace consists exclusively of the development of parts of the 

 endo-skeleton, viz. the neural spines and vertebral ribs (pleurapo- 

 physes)i agreeably with the opinion of Cuvier and Bojanus, and 

 that the remainder of the thoracic-abdominal case, consisting of the 

 "marginal pieces" and "plastron," are formed entirely from bones 

 of the dermal system. 



Adverting to the hypotheses of Cuvier, Geoffroy and Meckel, that 

 the thoracic-abdominal case is a modification of parts of the endo- 

 skeleton exclusively, the author tests their determinations by com- 

 parisons with the corresponding parts of the bird and crocodile, and 

 infers, from the latter animal, that the hyosternal, hyposternal and 

 xiphisternal bones are not parts of the sternum, but are homologous 

 with the hsemapophyses (sternal ribs and abdominal ribs); those in the 



