TELEOSTS (BOKY FISHES). 



The great majority of the forms which we ordinarily call 

 fishes belong to the group of Teleosts or bony fishes, so 

 called from the abundant bony matter in the skeleton. In 

 all, the mouth is at the tip of the snout, the nostrils on the 

 upper surface, and the caudal fin, though heterocercal in 

 the young, is homocercal in the adult. The skull is covered 

 with numerous bony plates, and the body is covered with 

 either cycloid or ctenoid scales. Sometimes (trout) scales 

 are apparently lacking, but this apparent absence may be 

 due to their small size and their being buried in the skin. 

 The gills are covered by an operculum. Of the internal 

 features which characterize the group may be mentioned 

 the absence of a spiral valve in the intestine, the presence 

 of an arterial bulb in the heart, and, very frequently, of a 

 swim-bladder. 



The thousands of species of bony fishes are variously 

 subdivided by naturalists accordingly as different structures 

 are made the basis of classification. One of the simplest 

 of these schemes recognizes six of these subdivisions or 

 orders, and is adopted here. To which does the specimen 

 you studied belong ? 



ORDER I. PHYSOSTOMI. 



Bony fishes in which the gill-filaments are arranged on 

 the branchial arches like the teeth of a comb; with the pre- 

 maxillary and maxillary bones movable (p. 10) ; the dorsal, 

 anal, and ventral fins supported only by soft rays (p. 9) ; 



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