THE FINGE-FINNED GANOIDS 2893 



longing to the true skeleton more or less fringed with dermal rays, the caudal fin 

 being either of the diphy cereal or heterocercal type- A pair of large jugular plates, 

 bounded in some instances by a series of smaller lateral ones, and an anterior un- 

 paired element, are developed in the branchiostegal membrane to fill up the space 

 between the two branches of the lower jaw, and thus representing the branchioste- 

 gal rays of the first order. In all the scales are coated with ganoine, although they 

 may be thin, overlapping, and rounded, or thick and quadrangular. The existing 

 forms have the optic nerves simply crossing one another, a spiral valve in the intes- 

 tine, and a duct to the air bladder; the presence of the latter being also shown in 

 certain extinct types. Next to the sharks and rays, this group is one of the oldest, 

 being well represented in the Devonian. 



The sole existing survivors of this great group of fishes are the 

 bichir {Polypterus bichir} of the Nile, and other rivers of tropical 

 Africa, and the reed fish {Calamoichthys calabaricus) from Old Cala- 

 bar; these constituting the family Polypteridce , which has no fossil representatives, 

 and probably forms a subordinal group by itself. In this family the notochord is 

 more or less constricted and replaced by ossified vertebrae; the baseosts, or superior 

 supporting elements, are rudimentary, or wanting, in the median fins; whereas the 





THE BICHIR. 



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 finlets, each formed by a spine 

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

 cereal 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 characterizing 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 four feet. Nothing is known of its habits. 

 The reed fish is a smaller form, characterized by the great elongation of the body, 

 and the absence of pelvic fins. 



Very little can be said here as to the numerous extinct representatives of this 

 group. One subordinal group (Actinistia) is represented by the hollow-spined 

 ganoids (Ccelacanthida:*) , which range from the Carboniferous to the Jurassic, and 



