POLYPTERUS. 



43 J 



of Lepidosiren " have been kept in captivity, but none have 

 shown a tendency to leave the water." 



The modern Dipnoi represent the Devonian fishes Holop- 

 tychius, Dipterus, and Phaneropleuron, 

 and the American Dinichtliys Torrelli 

 of the Devonian rocks of Ohio, which 

 is said by Newberry to have been about 

 five metres (from fifteen to eighteen 

 feet) in length, and a metre in thickness, 

 being inferior only in size to the Aster o- 

 lepis, a Placoderm of the old red sand- 

 stone of Great Britain. 



Order 3. Brancliioganoidei. Here be- 

 longs the Polypterus of the Nile and 

 Senegal. In these Ganoids the tail is 

 either protocercal or heterocercal ; the 

 scales are cycloid or rhomboid. The 

 dorsal fin is long, subdivided into divis- 

 ions, each with a separate ray and spine. 

 Polypterus licliir Geoffroy (Fig. 397) 

 has a protocercal tail. The young has 

 external gills (Fig. 393). It inhabits the 

 river Nile, P. senegalus the Senegal. 

 Calamoichthys differs in having no ven- 

 tral fins and in its elongated form. It 

 inhabits the rivers of Old Calabar. Al- 

 lied to these living forms are the De- 

 vonian Osteolepis, Ccelacanthus, and Ho- 

 loptychius. 



Order 4. Hyoganoidei. This group is 

 represented by the garpike and Arnia or 

 mud-fish of the United States, which 

 is an annectant form connecting the 

 Ganoids with the Teleosts. In these 

 fishes the spinal column is bony, the 

 tail partially heterocercal. 



In Lepidosteus (Fig. 398, L. osseus Agassiz) the body is 

 long, the jaws long and armed with sharp teeth, the vertebrse 

 are opisthocoelous, and the scales are large and rhomboidal, 



Fij*. 397 '.Polypterus bi- 

 chir. From Ctivier. 



