642 PHYLUM CHORDATA : CLASS PISCES — FISHES 



the Gambia ; and Lepidosiren^ from the swamps of the 

 Amazon basin. This discontinuous distribution is note- 

 worthy. 



They are very ancient forms. The genus Ceratodus 

 is abundantly represented by fossils in the Mesozoic 

 beds of Europe, America, Asia, and Austraha. There 

 were also undoubted Dipnoi far back in Palaeozoic times, 

 such as Dipterus and Phaneropleuron of the Devonian, 

 Ctenodus and Uronemus of the Carboniferous. They ex- 

 hibit many primitive features, e.g. in skeleton, limb struc- 

 ture, teeth, and spiral valve, and at the same time such 

 highly specialised characters as the use of the air-bladder 

 as a functional lung, cycloid scales, a very glandular skin, 

 and an arrangement of heart and circulatory system ap- 

 proaching that of higher Vertebrates. 



Fig. 367. — The Queensland lung-fish {Ceratodus forsteri). — From 



a Specimen. 



Appearance and Habits. — (i) Ceratodus. — Like that 

 other old-fashioned Australian animal the duckmole. 

 Ceratodus frequents the deep, still places of the river's bed, 

 where it lies sluggishly at the bottom, occasionally rising 

 to the surface to gulp in air, and making a grunting sound. 

 The body is stout and cylindrical, flattened posteriorly 

 from side to side, and covered with large round scales. 

 It may attain a length of 6 ft. The paired fins are thick 

 and trowel-like (Fig. 372). There are fi.ve gill-clefts 

 covered by an operculum, but no external gills. It crops 

 the luxuriant vegetation of the river-banks to obtain the 

 associated molluscs, crustaceans, worms, insect and fish 

 larvae on which it lives. Though Ceratodus cannot live 

 out of water — in the same way as other Dipnoi — it can 

 survive in pools laden with rotting vegetable matter by 

 taking mouthfuls of air at the surface. The eggs, about 



