Placdides. 47 



broad cutaneous plates, and which in their dentition nearly 

 approach the true type of the family of Celacanthes, that is 

 to say, of that of Holoptychius, Platygnathes, and Phyllole- 

 pis. The species of these two groups were evidently the 

 absolute sovereigns of the seas which they inhabited ; the 

 gigantic dimensions of the bodies of some of them and their 

 sharp cutting teeth gave them, there can be no doubt, an in- 

 disputable superiority. Already in the following strata, in 

 the coal formation, these tyrants of the primitive ocean are 

 accompanied by true Sauroides of remarkable size, the Me- 

 galichthys, for example, as well as others, although the Ho- 

 loptychius, Phyllolepis, &c., still exist along with them ; in 

 the succeeding formations, however, the Sauroides evidently 

 take the lead. The dentition of the Celacanthes of the old 

 red sandstone is very remarkable ; all these fishes, save 

 Glyptolepis, which likewise form a distinct group by their 

 fins, have needle-shaped, insulated teeth, placed at distances, 

 and formed of folded dentine ; and in no other group of the 

 animal kingdom does this folding of the dentine go so far as 

 among our Celacanthes ; witness the genera Dendrodus, 

 Lamnodus, &c. 



The Placdides of the old red sandstone are not yet suffi- 

 ciently known, in their organization, to enable us at present 

 to fix their relations to those of the following formations and 

 to those of the present creation. The fact which has struck 

 me most, in regard to them, is the small size of the Ichthyo- 

 dorulites of this formation compared with those of the coal 

 epoch and of the lias ; and, on the other hand, the rarity of 

 the teeth of these animals, relatively to the abundance of 

 their spiny rays, the very reverse of what we witness in the 

 cretaceous and tertiary formations, as well as among living 

 species. I conclude from this, that, in the early times of the 

 development of life, it was not so much the Placoides as cer- 

 tain Ganoides, Celacanthes, and Sauroides in particular, 

 which were the terror of the seas, and which traversed it 

 everywhere as masters, like the sharks of our own days, 

 under all latitudes. The approximations I have afterwards 

 made between the Placoides of the old red sandstone and the 

 sharks of the Mediterranean shew, that, in their numbers and 



