5i8 



FRINGE-FINNED GANOIDS. 



axonosts, or inferior supports, form a regular series equal in number to the dermal 

 fin-rays with which they articulate. The scales are ganoid, and the fins without 

 fulcra. The dorsal fin is divided into a number of Unlets, each formed by a spine 

 in front and a series of rays behind; the anal fin being situated close to the 

 diphycercal caudal, and the vent near the end of the tail, while the whole caudal 

 region is very short. In the bichir the body is moderately elongated ; the teeth 

 are rasp-like, and arranged in broad bands in the jaws and on the vomers and 

 palatines, the jaws also bearing an outer series of larger pointed teeth ; and the 

 pelvic fins are well developed, but do not show the obtusely lobate structure 

 characterising the front pair. The large air-bladder is double. The bichir is 

 found in the Upper Nile and the rivers on the west coast of Tropical Africa, 

 examples being occasionally carried down into the Lower Nile. The number of 

 finlets varies from eight to eighteen, and in size this fish grows to as much as 

 4 feet. Nothing is known of its habits. The reed-fish is a smaller form, charac- 

 terised by the great elongation of the body, and the absence of pelvic fins. 



Very little can be said here as to the numerous extinct repre- 

 Extinct Families. . . .... 



sentatives of this group. One subordinal group (Actinistia) is 



represented by the hollow-spined ganoids (Coelacanthidce), which range from the 



SKELETON -OF A HOLLOW-SPINED FRINGE-FINNED GANOID, Undina. 



(From A. S. Woodward, Cat. Foss. Fish, Brit. Mus.) 



Carboniferous to the Jurassic, and are best known by the genera Ccelacanthus and 

 Undina. In these fishes (as shown in the accompanying figure) the notochord 

 persists ; the axonosts of the anal and two dorsal fins are fused into a single piece ; 

 in the caudal fin the dermal fin-rays are each supported by a series of axonosts, 

 equal in number to the upper and lower spines of the vertebrae ; and each pelvic 

 has a single axonost, which is not united with that of the opposite side. In these 

 fishes the body is deeply and irregularly fusiform, with the scales overlapping, 

 rounded, and more or less coated with ganoine. There is a gill-cover and a single 

 pair of jugular plates ; the paired fins are obtusely lobate ; the tail is diphycercal, 

 frequently with a small supplemental fin at the extremity; and the air-bladder 

 is ossified. A third suborder (Rhipidistia) includes most of the other forms, 

 especially those from the Devonian formation, and while agreeing with the 

 preceding group in having a more or less completely persistent notochord, and 

 the axonosts of the anal and two dorsal fins each fused into a single piece, differs 

 in that in the caudal and other median fins the baseosts are fewer in number than 



