Vlll INTRODUCTION. 



accords with the conclusions arrived at many years ago by Sir 

 Richard Owen. In the Dinosauria the classification of Prof. 0. C. 

 Marsh has been adopted with some slight simplifications, such as 

 the union of the Stegosauria with the Ornithopoda. 



In the present work a few alterations have been introduced into 

 Dr. Baur's scheme. Thus, in order to make the value of the divi- 

 sions used among the Lacertilia and their allies more nearly equiva- 

 lent to those employed in the Dinosauria, it has been considered 

 advisable to group the true Lacertilia, the Rhiptoglossa, Ophidia, 

 and Pythonomorpha in a single ordinal group under the name of 

 Squamata — an association which was suggested by Prof. Cope on 

 page 308 of his work entitled ' The Origin of the Fittest' \ 



In deference, moreover, to the views of Prof. Seeley, the Protero- 

 sauria have been provisionally allowed an ordinal rank ; although 

 the writer is not by any means assured that this view will eventually 

 be maintained. Following also the views of the same writer, the 

 order Proganosauria of Baur is not retained, since the genus on 

 which it is founded appears to be clearly allied to the Triassic 

 Sauropterygia. 



In regard to the association of the Ornithosauria, Dinosauria, and 

 Crocodilia into a single branch there can be no question whatever ; 

 but some divergence of view may be legitimately entertained as to 

 the mutual association of some of the other orders. On the latter 

 grounds, coupled with the circumstance that when we trace back 

 the different branches in which the orders are here arranged into 

 the Trias and Permian we find all of them showing more or less 

 intimate relationships with one another, it has been considered inad- 

 visable, as already observed, to rank these branches as subclasses. 



The study of Fossil Reptiles, when contrasted with that of Fossil 

 Mammals, is found to suffer from the want of a common standard 

 of comparison, like that afforded by the teeth and jaws, on the evi- 

 dence of which by far the greater number of fossil mammalian 

 genera and species have been founded. In Reptiles, on the other 

 hand, genera and species, even in the same groups, have been 

 founded upon totally different parts of the skeleton, which do not 

 admit of comparison with one another. This renders it in many 

 groups almost or quite impossible to say how many genera or species 

 are/ really entitled to distinction ; and consequently entails the 

 introduction into a work liko the present of a considerable number 

 of names which may prove to be only synonyms. It has, moreover, 

 been thought advisable to retain such doubtful genera and species in 



3 8vo, London, 1887. 



