274 BRITISH FOSSIL REPTILES. 



it had no such near affinities to any of the existing genera, as to have constituted a 

 link intermediate between any two of them ; but tliat it manifested a type of the 

 Lacertian organisation, representing a division of the Order Lacertilia, adapted for 

 marine hfe, equivalent in character to the remainder of the Order as represented by the 

 existing terrestrial species ; and I have, therefore, indicated those two divisions or 

 tribes of the Order Lacertilia by the terms Natantia and Bepentia. 



The Lacertian Order expands as our survey of its existence in past time extends 

 backwards; and the same direction of development becomes more striking as we carry 

 our retrospect over the whole Reptilian Class. A new Order, with an organisation 

 more expressly adapted for marine life than in the Mosasaurus, comes into view when 

 we descend to the Chalk-beds, where it is represented by the remains of the Ich- 

 thyosauri and Plesiosauri described in the Fourth Chapter of the present Section. 

 Evidence of another Order of Reptiles, distinct from any now left to us, was 

 given by the discovery of the Iguanodon in the Green-sand of Maidstone. But the 

 most striking modification of the Reptilian structures is afforded by those remarkable 

 specimens of Pterodactyles, discovered in the Middle-chalk itself, and described in the 

 Fifth Chapter of the present Section. 



Succeeding Sections devoted to the Fossil Reptiles of still older Strata will 

 bring to light additional and varied forms of Enaliosauria, Ptcrosauria, and 

 Dinosauria, and also of tribes of Crocodilia no longer existing. All these modi- 

 fications of the once richly developed Class of Reptiles perished, according to 

 our present evidence, during the period of the deposition of the Chalk Formations, 

 after which we know that the seas of our Planet were peopled with carnivorous 

 fish-like animals of the warm-blooded Mammalian Class, and its dry land with 

 large herbivorous and carnivorous quadrupeds of the same highly-organised type. 



In considering the marvellous fact of the disappearance or extinction of the Orders 

 Enaliosauria and Pterosauria, we must bear in mind that the last Ichthyosaur of which 

 we have been enabled to get cognizance preserves as strictly the type of its peculiar 

 genus as any of its predecessors, and that in respect to the extent of cement outside 

 its teeth, which is such as to lead to their being wedged squarely into their common 

 alveolar groove, the Ichtlnjosavrus cami^jlodon, instead of showing any approach or 

 affinity to later forms of larger Peptilia, manifested a distinctive characteristic of its 

 peculiar genus in an exaggerated degree. So likewise with regard to the Flying 

 Reptiles, these seem at no period to have been represented by species so gigantic and 

 formidable as during the most recent of the Secondary Formations ; and the Order 

 Pterosauria, instead of showing signs of progressive decay or transmutation, seems to 

 have attained its highest and most typical development at the eve of its final 

 extinction. 



