248 PICTURESQUE SKETCHES 



very large, at least in some species, while the vertebrae 

 are short, and the ribs slight. The jaws are covered 

 with a band of very fine teeth, like the hairs in a 

 brush. The scales are jagged like the teeth of a 

 comb, and the fish belongs, therefore, to the ctenoid 

 order, of which that structure of the scales is charac- 

 teristic. 



The cycloid fish Osmeroides is also common in the 

 chalk, but belongs rather to the lower than the 

 upper beds. The fishes of this genus are very beau- 

 tiful, and often tolerably perfect, but their size is not 

 large. Fishes of the carp family, others allied to the 

 mackarel, and an eel-shaped fish called Dercetis, form 

 the remaining groups most abundant in the chalk, 

 and most characteristic of the formation. 



The reptilian remains of the cretaceous series are 

 exceedingly few, and present but a scanty amount of 

 new material with reference to this department of 

 fossil natural history. They include, however, one 

 new and gigantic lizard of marine habits, nearly allied 

 to the monitors (Mosasaurus) ; and with this are 

 found a few remains of turtles, one very gigantic 

 saurian whose structure is little known but which 

 has been called PolyptycJiodon (occurring in the lower 

 beds), the remains of a few Ichthyosauri, and frag- 

 ments of a Pterodactyl. 



Of these reptiles, that which has been named Mosa- 

 saurus (the saurian of the Meuse, on whose banks the 

 fossil remains of it have chiefly been found) resembled 

 the monitor of India and Egypt, especially in the struc- 

 ture of the head and teeth ; but the head alone is far 

 larger than the whole body of any existing species of 

 these animals, and the teeth, which are of proper- 



