THE 



FISHES OF THE NILE 



CROSSOPTERYGXL 



CLADIST1A. 



POLYPTERID.E. 



Sole survivors of an Order abundantly represented from the Devonian to the 

 Cretaceous, these Pishes are confined to the fresh waters of Africa, where they 

 form two genera — Folypterits, Geoffroy, of which three species live in the Nile ; and 

 Calarnichthys, J. A. Smith, a serpentiform type in which the ventral fins have 

 disappeared, and of which only one species is known, C. calalaricus, J. A. Smith, 

 inhabiting the Niger Delta, Old Calabar, Cameroon, and the Chiloango. They are 

 easily recognized by their armour of large rhombic bony scales coated with a layer 

 of enamel-like substance (ganoid scales), the presence of a pair of jugular plates, 

 replacing the branchiostegal rays, the presence of true clavicles, the lobate, pedunculate 

 pectoral fins, with three basal endoskeletal elements, and the dorsal fin forming a 

 series of isolated rays or finlets. 



Spiracles, covered by a bony valve, open on the top of the head. The air-bladder is 

 double, with the duct opening on the ventral side of the pharynx, and acts as an 

 accessory respiratory organ ; the heart has a conus arteriosus with several rows ot. 

 valves, and the intestine is provided with a spiral valve. 



B 



