422 Royal Society. 
Fam. PHOCIDA. — 
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. Pxocrna. 
No postorbital process. No ali-sphenoid canal. 
Mastoid process swollen, and seeming to form part of the auditory | 
bulla. 
Morunga. Lobodon. 
Cystophora. Leptonyx. 
Halicherus, 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 Chelonia, 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), 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 hemapophyses (sternal ribs and abdominal ribs); those in the 
Ss a oats We ne 
