72 PICTURESQUE SKETCHES 



with naked enamel ; a row of thickly-set pointed 

 teeth fringed the lips, and within this row was another 

 whose bulk was at least twenty times as great. The 

 other genus (Megaliclitliys) was perhaps more strik- 

 ingly characteristic of the next succeeding period, 

 during which the carboniferous limestone and coal 

 were being deposited, and it may therefore be as well 

 to postpone for the present any description of it. 



On the whole, it appears, then, that this second 

 period is at least as remarkable for the number and 

 variety of the remains of fishes found in the beds 

 which represent it as the former was for the frag- 

 ments of corals, shells, and other animals of infe- 

 rior organization. There seems at present no reason- 

 able way of accounting for this but by supposing, that, 

 until a certain time, commencing in England with 

 the mud-stones of the silurian rocks, fishes had not 

 been introduced upon the earth, and that when intro- 

 duced they were at first few, and afterwards increased 

 both in number and variety. The fact, however, that 

 among the forms of these animals first met with we 

 have several representatives of the tribe of sharks, 

 and also of some of the bony fishes of singular com- 

 plexity of organization, * is a sufficient answer to any 

 idea that might be entertained of a gradual advance 

 towards perfection of structure, even if we did not 

 see in the order of their introduction ample reason to 

 disprove any such notion. The singular family con- 

 taining the Pterichthys and Coccosteus, now that it 

 has been fully examined, exhibits also no approach in 

 structure and but little analogy to the lower tribe 

 of Invertebrata. 



* Agassiz, Monographic des Poissons Fossiles du Vieux Ores Rouge, 

 p. 32. 



