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PISCES 



Subclass Teleostomi. Order 1. Crossopterygii. {Long-finned 

 Ganoids.) — Polypterus bichir {Senegalus) (Figure 117) lives in the 

 deeper waters of the Nile (Harrington), but does not bury itself in 

 the mud like true mudfishes. The air bladder is an accessory- 

 respiratory organ. It is connected by a primitive trachea with the 

 pharynx and used as a lung. The larva of Polypterus resembles 

 amphibian larvae. It has external gills, and utilizes its pectoral 



Fig. 117. Polypterus bichir. Ganoid. /, full length lateral view of 44 cm. 

 Polypterus bichir. X i. la, dorsal view of mid-dorsal line of same. X i. /^, 

 lateral view of anterior portion of trunk of same, with pectoral fin removed. X i. 

 ic, ventral view of anal fins of same. X i. (Courtesy of Amer. Mus. of Nat. Hist.) 



appendages as supports. The median fin is primitive like that of 

 the tadpole, but differs in that it has cartilaginous supports or rays. 



Calaniichthys., the other genus of Crossopterygii, has an eel-like 

 shape, and lives in small muddy streams in middle western Africa, 

 feeding mainly on Crustacea. The Paleozoic Crossopterygii are 

 regarded as probable ancestors of the terrestrial vertebrates and the 

 present day fishes. 



Order 2. Chondrostei. — This order has a skeleton largely 

 cartilaginous, with ganoid scales and a heterocercal tail. 



The paddlefish or spoon-bill {Poly don) lives in the Mississippi 

 River and its tributaries. . It may reach a length of six feet and 

 weight of one hundred fifty pounds. It is sluggish, feeding on 

 mud, shoveled up with its spoon-bill snout, which is equipped with 



