2894 



THE BONY FISHES AND GANOIDS 



Extinct 

 Families 



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 bod)'- 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 jug- 

 ular 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 in the dermal fin rays, by which they are 



SKELETON OF A HOI.LOW-SPINED FRINGE-FINNED GANOID (Undina). 

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



overlapped. The suborder is represented by three well-defined families. In the first, 

 which is typified by the genus Holoptychius, the lobes of the pectoral fins are long 

 and acute, while the teeth have complex infoldings of the outer layer, somewhat 

 after the manner of those of the primeval salamanders, and the scales are thin and 

 cycloidal. The second family, of which Rhizodus is the typical genus, differs by the 

 lobes of the pectoral fins being shorter and blunter, and also by the less complicated 

 infoldings of the teeth. To this family belongs Gyroptychius from the Devonian or 

 Old Red Sandstone of Scotland. While agreeing with the last in the obtusely 

 lobate pectoral fins, the third family, as represented typically by Osteolepis of the 

 Old Red Sandstone, is characterized by the walls of the teeth being slightly infolded 

 only at their bases, and by the scales being of the true quadrangular ganoid type. 

 Remains of these fishes occur in extraordinary abundance in the Old Red Sandstone 

 of Scotland; and as this deposit is of fresh- water origin, it is evident that they were 

 either fluviatile or lacustrine forms. The reason why these and so many other 

 ancient creatures were enveloped in coats-of-mail has not yet been discovered. 



