Fossil Fishes. 35 



kinds of shagreen of the shark. It comprehends the cartilaginous 

 fish of Cuvier, with exception of the sturgeon tribe. 



" Order II. Ganoides. — This order comprehends families appa- 

 rently very different from each other, but which, notwithstanding, 

 when minutely examined, have many points of agreement. The 

 character common to them all is the angular form of their scales, 

 which are composed of two substances, one of corneous or bony la- 

 minas, superimposed on each other, and covered with a thick coat of 

 enamel. These scales are constructed precisely like the teeth. In 

 this order are arranged the Lepidoides, Agass., all of which are 

 fossil; the Sauroides, Agass., fossil, with the exception of two gen- 

 era, yiz. the Lepidostees and the Bichir ; the Pycnodontes, Agass., 

 also fossil ; the Sclerodermes, Gymnodontes, Lophobranches, Goni- 

 odontes, Siluridce, and Sturiones. 



" Order III. Ctenoides.— In this order the common character 

 consists in their laminated scales being toothed at their posterior 

 edges — those which are externally visible. The teeth of these nu- 

 merous laminae, which are so placed above each other that the low- 

 er always project over the upper, make the scales rough to the 

 touch. This structure is particularly obvious in the Chetodontes 

 and Pleuronectes. In this order are arranged the Percoides, Polya- 

 canthes, Scienoides, Sparoides, Scorpenoides, and Aulostomes. 

 There are the Anthopterigians of Cuvier and Artedi, with exception, 

 however, of those having smooth scales, and with the addition of the 

 Pleuronectes. 



" Order IV. Cycloides. — The families belonging to this order 

 are provided with scales formed of simple laminae with smooth edges, 

 a circumstance which does not prevent their external surface being 

 frequently ornamented with different designs, which are imprinted on 

 all the laminae, where they are exposed to view and are not covered 

 over. The scales of the lateral line are formed like all the others; 

 but, in place of being mere laminated plates, these are funnels, pla- 

 ced the one within the other, and of which the narrow part, applied 

 to the disc of the scale, forms a tube, from which the mucus which 

 covers the fish is poured out. This tube is sometimes bifurcated, or 

 even ramified. In this order are placed the Labroides, Muges, 

 Atherines, Scomber aides, Gadoides, Gobioides, Murenoides, Luci- 

 oides, Salmones, Clupes, and Cypri7iid(e." 



If we estimate the number of species of fishes, now known to 

 amount to about 8000, we may state that more than three-fourths of 



