358 



A HISTORY OF FISHES 



is the transformation of the walls of the air-bladder into bony 

 tissue. Quite recently one of these fishes was described, in 

 which the remains of several embryos could be seen in situ, thus 

 indicating that the manner of reproduction was viviparous. 



The Dipneusti may be readily distinguished by the character 

 of the teeth, which take the form of a pair of large plates with 

 coarse ridges situated on the roof of the mouth, and a similar 

 plate on the inside of each lower jaw (Fig. 130). Like the 

 Rhipidistia they flourished throughout the Palaeozoic era, but 

 dwindled during the Triassic period, from which time onwards 

 they were represented by forms not very unHke the existing 

 Lung-fish (Epiceratodus) of Australia (Fig. 99c). One of the 

 earliest members of the order is the interesting Dipterus, found 



Fig. 129. 

 Restoration of Undina giilo (Coelacanthidae), 



about \. (After Woodward.) 



in the Old Red Sandstone of Scotland along with the early 

 Rhipidistians and Palaeoniscids. In the ganoid scales, hetero- 

 cercal tail and two dorsal fins, this fish resembles the Osteo- 

 lepids, and the head is covered with a number of small bones. 

 The later Lung-fishes of the Ceratodus type appear to have been 

 almost world-wide in their distribution during the Triassic 

 period, teeth and other fragments having been found in 

 England, Europe, South Africa, India, and North America. 

 The surviving Australian genus (Epiceratodus) occurs only 

 in the fresh-water portions of the Burnett and Mary Rivers 

 of Queensland, but the presence of teeth of this genus in the 

 later Tertiary deposits of New South Wales indicates a wider 

 distribution in comparatively recent times. The other existing 

 Lung-fishes were probably derived from some form like Ceratodus, 



