266 CHARACTERS OF VERTEBRATE ANIMALS 



paired fins are even narrower than those of Protopterus, and 

 supported only by a central jointed axis. 



Sub-class II.— BONY FISHES (Teleostomi) 



This large group of fishes includes a vast number of recent 

 and fossil forms which present such varying characters that it 

 is difficult to give a satisfactory definition. There is, however, 

 a good deal of bone in the skeleton, and the jaws, instead of 

 being mere bars of gristle, as in a Dog-Fish, are ensheathed by 

 tooth-bearing bones in the same way as in higher forms. The 

 gill-clefts are very near together, and the gill-arches between 

 them are comparatively narrow, so that the gill-folds as seen 

 in a Dog-Fish are not supported along the whole of their length, 

 but project more or less to the exterior as free gill filaments. 

 The gill-clefts are covered over and protected by a flap, the 

 gill-cover or operculum, which is supported by bones. Two 

 orders may be distinguished: — i. Ganoids, and 2. Bony Fishes 

 proper or Teleosts. 



Order i. — Ganoids (Ganoidei) 



Under this name are included a number of recent genera, 

 widely scattered over the globe, and for the most part limited 

 to fresh water (fig. 162). They are the last surviving remnants 

 of groups which were once of great importance, but which have 

 been unable to compete with more highly- organized fishes, and 

 have greatly declined in consequence. Of recent forms the 

 two most primitive are the Bichir {Polypterus) of the Nile and 

 some other African rivers, and the Reed- Fish (Calamoichthys) 

 from the rivers of Old Calabar. The former is a remarkable- 

 looking creature of respectable size, being as much as 4 feet 

 long. Running along the back are a considerable number of 

 little dorsal fins, each with a strong spine in front, while the 

 last of them abuts against the rounded protocercal fin of the 

 tail, close to which, on the under side, is an anal fin. The 

 paired fins consist of a thickened basal part, supported by 

 cartilages something like those described for Dog-Fish (see p. 261), 

 and fringed by a thinner region supported by radiating fin-rays. 

 The body is covered by thick lozenge-shaped bony plates (ganoid 



