CHAPTER III 

 THE BONY FISHES AND GANOIDS SUBCLASS TELEOSTOMI 



FORMERLY the typical bony fishes of the present day were regarded as indica- 

 ting a primary group (Teleostei) of equal rank with a second one known as the 

 Ganoidei; the latter, containing the American bony pike, and the African bichir, to- 

 gether with a host of extinct genera possessing a similar armor of hard ganoid 

 scales. A fuller study of these and other allied fossil forms has, however, shown 

 the existence of such a complete transition from these so-called ganoids to the typical 

 bony fishes that it has become necessary to include the whole of them in a single 

 subclass, under the title heading this chapter. Although there is still some degree 

 of uncertainty as to the best mode of arranging certain groups of the bony fishes, 

 the following scheme may be temporarily adopted: 



1. Order ACTINOPTERYGII Fan-Finned Group. 



(1) Suborder p f ACANTHOPTERYGII Spine- Finned Fishes. 



(2) " I LOPHOBRANCHII Tuft-Gilled Fishes. 



u ^ 



(3) 8 I PLECTOGNATHI Comb-Gilled Fishes. 



(4) [ANACANTHINI Soft-Finned Fishes. 



(5) PHYSOSTOMI Tube-Bladdered Fishes. 



(6) ^THEOSPONDYLI Bony Pike. 

 ( 7 ) PROTOSPONDYLI Amioids. 

 (8) CHONDROSTEI Sturgeons. 



2. Order CROSSOPTERYGII Fringe-Finned Group. 



In this wide sense the subclass differs broadly from the two preceding ones in 

 the structure of the skull, which is formed on what may be termed the hinged type 

 (hyostylic) ; that is to say, the palato-pterygoid bar remains separated from the cra- 

 nium proper, to the hinder part of which it is movably articulated by the interven- 

 tion of the hyomandibular. The internal skeleton is more or less ossified, with the 

 development of membrane bones on the jaws; the gill clefts are but slightly separated 

 from one another, and are fully protected by an operculum ; the membrane bones of 

 the pectoral girdle (that is to say, the scapula, claviculars, etc.) are connected with 

 the hinder part of the skull; and the external skeleton takes the form either of 

 plates of bone or of calcified overlapping scales. In existing forms the eggs are 

 small, numerous, and generally massed together; the two optic nerves may 

 either simply cross one another, or may give off mutually interlacing fibres; an air 

 bladder with or without a duct is very generally present, and the intestine may 

 sometimes be furnished with a spiral valve. 



This group Actinopterygii includes all the bony fishes of the present day, 

 as well as the sturgeons, and is characterized by the fan-like structure of the paired 



(2701) 



