ORDER ELASMOBRANCHEI. 



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these, as their terminations indicate, having been applied to spines, 

 and others to teeth. 



Recent discoveries have enabled us to attain to a nearly complete 

 knowledge of the anatomy of this remarkable genus, and a restoration by 

 M. Brongniart of one of the species is shown in the accompanying wood- 

 cut. The skin was quite naked ; the body elongate, and the snout 

 obtuse. The teeth have a thick and depressed root, with a crown 

 formed by two unequal corners diverging like a V, with a small denticle 

 at the base of the two, and not unfrequently a minute flattened mammilla 

 posteriorly. In the male the pelvic fins carry a robust " clasper." At the 

 top of the head there was a large barbed spine (fig. 852, 1), with a double 

 row of serrations, and, according to the restoration (fig. 850), supporting a 



350. — Restoration of the skeleton of Pleuracanthus Gaudryi ; from the Carboniferous 

 of France, reduced. (After Brongniart.) 



cephalic fin. In the skull, according to Dr Koken, there was a distinct 

 hyomandibular, but the palatopterygoid bar had a direct connection 

 with the postorbital process of the cranium, as in Notidanus. Dr Koken 

 would slightly modify the structure of the pectoral fin from that given in 

 fig. 850. The dorsal fin is of great length, extending backwards as far as 

 the diphycercal caudal, from which it is separated by a deep notch. 

 According to M. Brongniart's restoration the anal fin was double, 

 and its two divisions had a structure curiously like that of limbs ; 

 Dr Koken considers, however, that the restoration is incorrect in this 

 particular. Specimens of the figured species attain a length of more than 

 a yard. 



In time this genus extends from the Carboniferous to the Lower 

 Permian ; while in space its range embraces both Europe and 

 North America. Chondrenchelys, from the Lower Carboniferous of 

 Dumfriesshire, which is provisionally referred to the same family, has 

 no cephalic spine. Detached teeth from the Keuper of Somerset, 

 described under the name of Diplodus, apparently indicate the sur- 

 vival of a form allied to Pleuracanthus in the Triassic period. 



Family CLADODONTiDiE. — The second family of this suborder is 

 too imperfectly known to admit of definition ; but it appears that in 

 the type genus the pectoral fin had only one series of rays, and was 

 thus intermediate between that of Pleuracanthus and the fins of 

 the Selachii. The type genus Cladodus had a broad and depressed 



