CLASSIFICATION OF KEPTILES. 6 



consideration, it is found that there are close approximations between 

 the two classes, and that the one group is probably descended from 

 the other. The descent is, however, not apparently to be traced 

 through a single line. On the contrary, while the great majority 

 of Reptiles seem to trace their origin to one extinct group 

 of Amphibians (the Microsauria), one particular extinct group of 

 the former, namely, the Theromorpha, shows evidence of descent 

 from a second group of Amphibians (the Labyrinthodonta). From 

 the first great branch of Reptilia, which includes all the " orders " 

 in the following table except the last, Birds seem to have been 

 derived ; so that the whole assemblage may be termed the Bird-like 

 Reptiles. 



The tenth order of Reptiles, on the other hand, which has been 

 long since extinct, exhibits remarkable indications of affinity with 

 Mammals, this being displayed in the character of the teeth, of the 

 skull, and of the limb-bones ; and it is probable that this group 

 represents the ancestral stock from which Mammals are derived. 

 Indeed, there are certain South African fossils in regard to which it 

 is difficult to say whether they should be referred to Reptiles or 

 Mammals. 



The following table exhibits the chief sub-divisions of the class 

 Reptilia, that is to say, the orders and sub-orders under which the 

 various families are arranged. Those groups which are extinct are 

 indicated by a f ; and it will be noticed that the proportion of these 

 extinct groups is very large indeed — much larger than in the case of 

 either Mammals or Birds. The explanation of this is that Reptiles 

 are a very ancient group, which attained its maximum development 

 when Mammals and Birds were in their infancy ; hence the extinc- 

 tion of a large number of groups. 



CLASSIFICATION OF REPTILIA. 



Order. Sub-order. Case. 



I. fORNITHOSAURIA . . . j . 



(Pterodactyles.) / ' " " 



(Dinosaurs.) ] 3 Omit f opoda . . . . ) 



3 I -r-r-r ,-, -n ( 1. Eusuchia 1 



6 | III. Ceocodilia, or Emydo- 2 +A etosauria ..... Q 



(Cr^diles.)' ■ ' ' [ 3- &£«£*+ « ^ j 



B 2 



