POLYPTERUS. 



431 



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

 shown a tendency to leave the water." 



The modern Dipnoi represent the Devonian fishes Holoj)- 

 ty chins, Dipterus, and Phaneropleuron, 

 and the American Dinichthys Torrelli 

 of the Devonian rocks of Ohio, which . 



is said by Ne wherry to have been about / <Cp, 



five metres (from fifteen to eighteen 

 feet) in length, and a metre in thickness, 

 iDeing inferior only in size to the Astero- 

 lepis, a Placoderm of the old red sand- 

 stone of Great Britain. 



Order 3. Branchioyanoidei. Here be- 

 longs the Polijpterux 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 bichir Geoffrey (Fig. 39?) 

 has a protocercal tail. The young has 

 external gills (Fig. 393). It inhabits the 

 river Nile, P. senegalus the Senegal. 

 Calamoiclithys 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- 

 Tonian Osteolepis, Ccelacanthus, and Ho- 

 loptychius. 



Order 4. Hyoganoidci. This group is 

 represented by the garpike and Ami a or 

 mud-fish of the United States, which 

 is an annectant form connecting the 

 Ganoids with the Teleosts. In these m ._ ftvptfrus . 



iishes the spinal column is bony, the chir. From cuvier. 

 tail partially heterocercal. 



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

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

 are opisthoccelous, and the scales are large and rhomboidal, 



