94 



Dipnoi Sirenoidei. 



Iscliyodus in the Stonesfield Slate, and the latter g*enus ranges 

 upwards to the Upper Cretaceous. Nearly complete skeletons 

 have been found in the Lithographic Stone of Bavaria. Eda- 



FIG. 128. Lower Jaw of Edapliodon leptognathus, Ag. ; Middle Eocene, Bracklesham Bay, 



Sussex. 



phodon (Fig. 128) and Elasmodus are Cretaceous and Eocene; 

 Chimcera dates back at least to the Pliocene. 



Wall-case, 

 No. 5, and 

 Table-case, 

 34. 



Sub-class III. DIPNOI. 



ORDER I. Sirenoidei. 



The typical Dipnoi (double-breathers) are so named because 

 in their living representatives the air-bladder assumes the 

 function of a lung, and thus furnishes them with a second 



FIG. 129. Skeleton of the African Mudfish, Protopterus annectens, living in the Rivers of 



Africa. 



means of respiration. They are a nearly extinct race, only 

 three forms now surviving, namely, Protopterus in Africa (Fig. 

 129), Lepidosiren in South America, and Ceratodus (Epiceratodus) 

 in Australia (Fig. 130). 



FIG. 130. "The Australian Mudfish," Ceratodus Forsteri (recent), Australia. 



The notochord in these fishes is always persistent, and the 

 tail is diphycercal or heterocercal. There are two pairs of 



