POLYPTERID.E ; AMIID.E. ORDER TELEOSTEI. 43 



599. In the POLYPTERID^E, or Fin-pikes, the body is also 

 covered with rhomboidal bony plates, but the fins are not furn- 

 ished with fulcra. The head has a pair of spiracles, and the 

 tail is slightly unsymmetrical. But the most singular character 

 presented by these Fishes is the structure of the dorsal fin, which, 

 instead of being continuous, is separated into a considerable num- 

 ber (twelve to sixteen) of strong spines, distributed at short in- 

 tervals along nearly the whole of the back, and each bordered 

 behind by a small soft fin. Two species of this curious group 

 are known, one of them inhabits the Nile, and the other the 

 Senegal. 



600. The AMIID^E, or Bald-pikes, forming the last family of 

 recent Ganoid Fishes, approach far more closely than the pre- 

 ceding Fishes to the ordinary bony fishes. The skin is covered 

 with small, rounded, horny scales, coated with enamel ; the cau- 

 dal fin is scarcely unsymmetrical, and is destitute of fulcra, as are 

 also the remainder of the fins; and even the peculiar structure 

 of the arterial bulb, and of the intestine, is exhibited with far 

 less distinctness than in the preceding groups, which may be re- 

 garded as the existing types of the order. The species of this 

 family, which are few in number and of small size, are peculiar 

 to the rivers of South America ; they are said to feed principally 

 upon small Crustacea. 



ORDER III. TELEOSTEI. 



601. We now come to the order of true Bony Fishes, which 

 may be regarded as the typical order of the class. The general 

 characters of the-e will be sufficiently understood from the com- 

 parative statements already given, but they may be shortly re- 

 capitulated as follows. The skeleton is almost always perfectly 

 ossified, the only exceptions to this rule being presented by a 

 few fishes, of which the skin is usually covered with bony plates, 

 in which the vertebral column and its appendages are cartila- 

 ginous ; but even in these the skull is completely ossified. The 



