PISCES. 



369 



Subclass III. Teleostei (Bony Fishes). -Fishes with well-ossified skele- 

 tons ; body covered with cycloid or ctenoid scales ; exoskeleton of bony 

 plates in the head region which become associated with bones of the 

 internal skeleton to form the skull ; mouth terminal rather than ventral ; 

 gills covered; spiral valve lacking; air-bladder usually present; homo- 

 cereal tail. 



This subclass embraces the great majority of the forms ordinarily 

 known as fishes. There are estimated to be 6,000 or more species of 



FIG. 184. 



FIG. 184. 



Long-eared Sunfish (Lepornis auritus). Adult. Photo from life by 

 Dr. R. W. Shufeldt. 



teleosts, more than 2,000 of which inhabit fresh water. The group is 

 variously divided by different authors and the student must be referred 

 to more advanced texts for fuller classification. The principal orders are 

 outlined below. 



Pneumatic duct (from air-bladder to intestine) open. ..Order Physostomi. 

 (Carp, cat-fish, sucker, salmon, trout, shad, herring, eel, etc.) 

 Pneumatic duct closed. 



Dorsal, anal, and pelvic fins spiny in front. 



Bones of the pharynx (branchial arches) distinct. 



Order Acanthopteri. 

 (Perch, sun-fish, mackerel, stickleback, silverside, etc.) 



Bones of the pharynx united Order Pharyngognathi. 



Dorsal, anal, and pelvic fins without spines Order Anacanthini. 



(Cod-fish, haddock, flat-fish, etc.) 



(Two other teleost orders of less importance, embracing some 

 very peculiar forms, are the Plectognathi (globe-fishes) and the 

 Lophobranchii (sea horses, Fig. 58; and pipe-fishes). 

 Subclass IV. Dipnoi (Lung-fishes). Fishes with a persistent notochord 

 and the internal skeleton incompletely ossified ; soft cycloid scales ; spiral 

 valve in the intestine, the swim-bladder used as a lung, the auricle partly 

 separated into two chambers, paired appendages with a central axis pro- 

 ducing a flapper rather than a fin (Fig. 174). There are only three or four 

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