18 SIRENOID AND CROSSOPTERYGIAN GANOIDS. 



ample knowledge of the structure of Lejpidosiren and Protopterus, Muller rested the 

 definition of his new sub-class, Dipnoi, upon the following characters •} — Scaly fishes with 

 both lungs and gills, and nostrils communicating with the mouth. Valves in bulbus arteriosus 

 placed longitudinally and spirally. Spiral valve in intestine. Oviducts opening into 

 abdominal cavity. Vertebral column with notochord and attached apophyses. The two 

 sentences in italics contain the marks which Muller understood to distinguish Dipnoi 

 from Ganoidei, and of these the first relates to adaptive characters alone. 



Family Ceratodontini, Giinther. 



Paired fins developed as broad, pointed paddles, supported by jointed, cartilaginous, 

 axial rods, which give off jointed rays on each side. Bulbus arteriosus with valves in 

 three transverse series. 



Genus Ceratodus, Ag? 



Skull. — A cartilaginous primordial skull, continuous with vertebral column, partially 

 ossified, covered from side to side by a bony shield, which is made up of two median 

 and several lateral plates. The temporal muscles separate the hind part of this shield 

 from the primordial skull. Palato-pterygoid ossified, supporting a dental plate, and 

 articulating with a downward process from the frontal part of the cranial roof. Suspen- 

 sorium chiefly cartilaginous ; a quadrate (?) ossification on its outer side ; hyomandibular 

 very small, unossified. A^omer represented only by the bony base of the "vomerine" 

 tooth. A large lozenge-shaped parasphenoid, enclosed between palato-pterygoids in front, 

 and extending backwards to about the level of the fourth vertebra. Nasal foramina two 

 on each side ; the anterior in front of the mouth, inferior ; the posterior external to 

 palatal dentary plates, partly surrounded by small labial cartilages. Opercular and 

 inter-opercular bones. Pre-opercular (?) united to bony shield. Mandible short, with 

 wide symphysis ; autostylic. Dentary, splenial, and angular pieces, the splenial supporting 



1 < Abh. Ak. Wiss. Berlin,' 1844, p. 198. 



2 It is my pleasant duty to return thanks for much kind help in the study of this genus. The Earl of 

 Ennisldllen, Sir Philip Egerton, Mr. E. B. Tawney and the Directors of the Bristol Museum, Dr. Oldham, 

 late Director of the Geological Survey of India, Mr. W. Davies, of the British Museum, and Mr. E. T. 

 Newton, of the Geological Survey of England, have allowed me to study the collections in their possession 

 or under their care to the greatest advantage, and have also, in some cases, materially assisted me by 

 information and advice. 



