THE IGUANODON AKD IGUANA, 361 



snbseqnent formation, till the present period, when we 

 find it represented by the large and savage inhabitants of 

 the Mississippi, the Nile, and the Ganges. 



What is still more to the purpose is, that the Igua- 

 nodon, a vast saurian which was contemporary with the 

 Plesiosaur and Ichthyosaur, though transmitting no ob- 

 served representative of its form through the tertiary 

 era, is yet weU represented by the existing Iguanadw of 

 the American tropics. 



It is true the Iguana is not an Iguanodon; but the 

 forms are closely allied. I do not suppose that the so- 

 called sea-serpent is an actual Plesiosaur, but an animal 

 bearing a similar relation to that ancient type. The 

 Iguanodon has degenerated (I speak of the type, and not 

 of the species) to the small size of the Iguana; the 

 Plesiosaurus may have become developed to the gigantic 

 dimensions of the sea-serpent 



A correspondent of the Zoologist.(p. 2395) adduces the 

 great authority of Professor Agassiz to the possibility of 

 the present existence of the Enaliosaurian type. That 

 eminent palaeontologist is represented as saying, that " it 

 would be in precise conformity with analogy that such an 

 aniflial should exist in the American seas, as he had 

 found numerous instances in which the fossil forms of 

 the Old World were represented by living types in the 

 New. He instanced the gar-pike of the Western rivers, 

 and said he had foimd several instances in his recent 

 visit to Lake Superior, where he had detected several 

 fishes belonging to genera now extinct in Europe." 



