DIPNOI. 97 



is an inhabitant of tropical Africa, occurring in abundance in the [Case 

 rivers of the West coast and in the Upper Nile. 



Lepidosxeoidei (Case 28). — The fishes of this group, as well as 

 the following, are remarkable for the hard, bony, lozenge-shaped, 

 polished {ganoid) scales with which they are covered. The skeleton 

 is nearly completely ossified. The dorsal and anal fins are composed 

 of articulated rays only, and placed far backwards, close to the 

 caudal. Though the end of the body appears nearly diphycercal 

 {i. e. with the caudal rays inserted above as well as below the 

 vertebral axis, as in the case of most Teleosteans), the termination 

 of the vertebral column is, in fact, distinctly heterocercal, as in 



Fig. 87. 



Gar-Pike of North America (Lepidosteus vindis). 



Sharks. The Gar-Pike {Lepidosteus, fig. 87) are at present limited 

 to the temperate parts of North America, Central America, and 

 Ctiba. They feed on other fishes. 



Dipnoi (Case 28). — The skeleton is notochordal. There are two 

 pairs of nostrils, more or less within the mouth. Their respiratory 

 organs are gills as well as lung-like sacs. The dentition is very 

 peculiar ; it consists of a pair of large molars, above and below, and 

 a pair of vomerine teeth. The molars, the upper pair of which are 

 inserted on a pterygo-palatine ossification, are provided with strong 

 cusps or lateral prongs. The vomerine teeth are conical, pointed, 

 or incisor-like. The fore limb diflPers greatly from the pectoral fin 

 of other fishes. It is covered with small scales along the middle 

 from the root to its extremity, and surrounded by a rayed fringe 

 similar to the vertical fin. A muscle split into numerous fascicles 

 extends all the length of the fin, which is fiexible in every part 

 and in every direction. The cartilaginous framework supporting 

 it is joined to the scapular arch by an oblong cartilage, followed by 

 a broad basal cartilage, generally single, sometimes showing traces 



