DIPNOI. 



175 



(Ceratodus) or contains, as in the frogs, two lateral spiral longitudinal 

 folds, which fuse at their anterior end and effect the division of the 

 lumen into two (for the branchial arteries and the pulmonary 

 vessels). 



Sub-order 1. Monopneumona. The body is covered with large 

 cycloid scales (fig. 619 a). Yomerwith two oblique incisor-like dental 

 lamellae. Palate armed with a pair of large and long dental plates 

 (molars), which have a flat undulated surface and five or six sharp 

 prongs on the outer side. Lower jaw with two similar dental plates 

 (fig. 619, c). Fins as in the Crossopterygii, with scaly shaft and 

 rayed border on each side (fig. 619, b). The valves in the conns 

 arteriosus rather resemble those of the Ganoids. 



FIG. 619. a, Ceratodus miolepi*. b, its pectoral fin (after Giinther). <, lower jaw with 

 dental plates of Ceratodus Forsteri (after Krefft). 



Branchial apparatus formed of five cartilaginous arches and four 

 gills. Pseudobranchs (hyoidean) are present. The lung is composed 

 of two symmetrical cellular halves. The two ureters open on the 

 dorsal side of the cloaca by a common opening. There is a pair of 

 wide peritoneal slits (abdominal pores) behind the anus. The Mono- 

 pneumona feed on leaves, which they tear off with their incisor teeth 

 and masticate with their molars. They make use of the lungs in re- 

 spiration principally when the muddy water is saturated with gases 

 from organic matter. They have existed since the Triassic period. 



Fam. Ceratodidae, with the single genus Ceratodus Ag. C. Forsteri Krefft, 

 (and miolepis Gunth.), the Barramunda, Queensland ; reaches a length of six 

 feet. Its flesh is salmon-like and much esteemed as food. 



Sub-order 2. Dipneumona. Fins narrow, with jointed cartilaginous 



