1 6 REPTILES 



reptiles, for which he suggests a dual origin from two distinct 

 groups of the Stegocephalia, namely the Labyrinthodontia on 

 the one hand, and the Microsauria on the other. 



Although in one sense such diversities of opinion are a 

 matter for regret, yet like political parties, they have their ad- 

 vantage, for in this particular instance they tend to show, even 

 in the present crude and imperfect condition of our knowledge, 

 the existence of a kind of border-land, or " buffer-state," between 

 stegocephalian amphibians and reptiles, some of the inhabit- 

 ants of which may be referred to the one or the other of these 

 groups according to the idiosyncracy of the particular writer 

 who may be attempting their classification. 



Assuming, then, that we are right (following Mr. Boulenger) 

 in dividing reptiles into two main divisions, or brigades, it may 

 be considered not improbable that while the mammal-like divi- 

 sion (Theromorpha) may trace its origin to the Labyrintho- 

 dontia, the bird-like brigade (Ornithomorpha) may have sprung 

 from the Microsauria. 1 



The Theromorpha, which appear to be confined to the Per- 

 mian and Triassic periods, are connected with the labyrintho- 

 donts by means of the Pariasauria, as represented by the huge 

 amphibian-like reptiles from the Trias of Africa and Russia 

 constituting the genus Pariasaurus. In this group the skull 

 was as completely closed in by roofing bones as in the labyrin- 

 thodonts (Fig. i ), but its under surface had lost the para- 

 sphenoid bone characteristic of amphibians in general. From 

 Pariasaurus there is a transition in one direction to the 

 Cotylosauria, as represented by Pariotichus, Empedias, 

 Diadectes, Pelcrpetum, and ProcolopJion which still have the 

 temporal region of the skull more or less completely roofed 

 over with bone, but which differed from the Pariasauria by the 

 greater number of joints in the toes. Some of these reptiles, 

 it may be remarked, had the cheek-teeth expanded transversely, 

 which suggests kinship with mammals, despite the fact that 

 the group appears to have died out without descendants, being 

 merely a side-branch from the Pariasauria. 



On the other hand, the latter group appears to have also 

 given rise to the Anomodontia, which apparently included, in 



1 Since this was written fuller details as to the relationships of the Micro- 

 sauria have been published by Mr. R. S. Moodie. 



