168 THE PROGRESS OF DEGRADATION. 



canths, and almost all the Dipterians,* runs througli the upper 

 lobe of the fin, and terminates in a point (see fig. 5 G), it must 



Ym. 56. 



TAIL OF OSTEOLEPIS. 



liave possessed the gradually diminishing vertebrae, or a di- 

 minishing spinal cord, their analogue ; but the rays, fairly set, 

 as their state of keeping in the rocks certify, exist as narrow 

 oblong plates of solid bone ; and their anterior edges are 

 strengthened by a line of osseous defences, that pass from scales 

 into rays. And in harmonious accompaniment with this fairly 

 stereotyped edition of the ichthyic tail, we find, in the fishes 

 in which it appears, the first instance of displacement of limh^ 

 — the bases of the pectorals being removed from their origi- 

 nal position, and stuck on to the nape of the neck. It may 

 be remarked in passing, that in the tails of two ganoidal 

 genera of this period, — ^the Coccosteus and Fterichthys, — the 

 analogies traceable lie rather in the direction of the tails of 

 the rays than in those of the sharks ; and that one of these, 

 the Coccosteus, seems, as has been already intimated, to have 

 had no pectorals, while it is somewhat doubtful whether in the 

 Fterichthys the pectorals were not attached to the shoulder, in- 

 stead of the head. In the Carboniferous and Permian systems 

 there occur, especially among the numerous species of the 

 genus Palceoniscus, tails of the type exemplified by the internal 



* The vertebral column in the genus Diplopterus ran, as in the plaooid 

 genus Scyllium, iiearly through the middle of the caudal fin. 



