1871.] Dr. A. Gtinther's Description of Ceratodus. 



377 



March 16, 1871. 



General Sir EDWARD SABINE, K.C.B., President, in the Chair. 

 The following communications were read : — 



I. " Description of Ceratodus, a genus of Ganoid Fishes, recently 

 discovered in rivers of Queensland, Australia/' By Albert 

 Gunther, M.A., Ph.D., M.D., F.R.S. Received February 7, 

 1871. 



(Abstract.) 



After some introductory remarks the author proceeds to give a descrip- 

 tion of the external characters which appear to indicate the existence of two 

 species, viz. Ceratodus forsteri, with fewer and larger, and Ceratodus 

 miolepis with smaller and more numerous scales. The microscopical 

 structure of the scales and teeth is treated of in two separate chapters, the 

 latter being compared with the fossils from the Triassic and Jurassic forma- 

 tions, and found to be identical. The resemblance to the dentition of 

 Protopterus, Psammodus, Bipterus and other fossil genera is pointed out. 



The skeleton resembles in its general characters, as well as in numerous 

 points of detail, so much that of Lepidosiren, that from this part alone the 

 conclusion must be drawn that these genera belong to the same natural 

 group of fishes. It is notochordal, all its parts having a cartilaginous 

 basis, more or less incompletely covered by thin osseous lamellae. 



The ossifications of the skull are but few in number, and may be desig- 

 nated thus : — ethmoid ; a pair of frontals separated by a single " sclero- 

 parietal" ; basal, with a tooth-bearing ptery go-palatine on each side, the 

 latter bones being suturally united in front ; vomer cartilaginous, tooth- 

 bearing. Maxillary and intermaxillary elements are not developed, re- 

 placed by facial cartilages which are confluent with the suborbital ring, all 

 these parts being cavernous. Tympanic pedicle cartilaginous, with ossified 

 lamella (os quadratum) and double condyle. Mandible with an articulary 

 and dentary lamella. Prccoperculum a rudimentary moveable cartilage. 

 A well-developed operculum and styliform suboperculum. Hyoid arch more 

 complex than in Lepidosiren, consisting of a pair of ceratohyals, a basi- 

 and glosso-hyal. Branchial apparatus composed of five arches, of which 

 the last is rudimentary ; not differing from the Teleosteous type, but car- 

 tilaginous. In a vertical section of the head the parts of the brain-cavity 

 and of the acoustic cavity (which is entirely enclosed in the skull) are 

 explained. A pituitary gland is present. 



The notochord forms the base for about 68 sets of apophyses, 27 of 

 which bear ribs. The various modifications in the different parts of the 

 column are described in detail ; and more especially attention is directed 

 to the first rib, which is very similar to that of Lepidosiren, where, from 

 its more intimate connexion with the skull, it was interpreted in various 



