58 FISH GALLERY. 



the other two families the vertebral axis is straight and the outline 

 of the tail symmetrical (diphycercal tail). A distinct anal fin is 

 present in the Phaneropleuridse and Dipteridse, and two separate 

 dorsal fins in the latter family. 



MONOPNEUMONES. 



Cerat- In the Monopneumones the lung, or modified air-bladder, is a 



odus. single organ ; it lies to the dorsal side of the alimentary 

 canal, hut opens into the ventral wall of the oesophagus. It 

 has a central cavity, communicating with air-cells or alveoli in 

 the thickness of its walls. The Ceratodus or Australian Lung- 

 fish, Ceratodus forsteri (171, and fig. 34), which is the sole 

 living representative of the order, lives in the stagnant pools 

 connected with the Burnett and Mary Rivers of Queensland. It is 

 sluggish in habit and feeds on crustaceans, worms and molluscs. 

 It has four pairs of well-developed gills by which aquatic respira- 

 tion is effected. In the dry season, when the water is thick and 

 foul, and to a less extent at other seasons also, the fish rises 

 occasionally to the surface to empty its lung-sac and to take a 

 fresh supply of air. The Ceratodus grows to a length of five or 

 six feet, and is excellent eating. It was first described in 1870 

 by Mr. G. Krefi% who recognised the teeth as similar to the teeth 

 of Ceratodus which had long been known in a fossil state from 

 the Jurassic rocks. The name 'Barramunda' is sometimes applied 

 to Ceratodus, but it is used indiscriminately by the aborigines for 

 any large fresh-water fish, and as often as not is applied to 

 Osteoylossum {Scleropages) leichardti. 



The paired fins of the Ceratodus are long and pointed, and each 

 consists of a middle, thick, muscular part or f lobe ', supported by 

 an axial series of cartilages, and two series of obliquely disposed, 

 smaller cartilages in connection with the former, and a fringe or 

 fin-membrane supported by numerous closely-set fin-rays of dermal 

 origin. This type of fin is known as the ' archipterygium \ and 

 was formerly regarded as a primitive type of fin. The tail is 

 reduced and symmetrical, and is continuous with the single dorsal 

 and anal fins. The cartilage of the skull is protected by a few 

 lariie bony plates, covered with skin. 



