INTRODUCTION. XV 



performed, and the animal resumes its former habits, with- 

 out having undergone any material change. 



I have already hinted at the difficulties which exist in 

 forming a consistent and unobjectionable arrangement of 

 these animals. The order of Testudinata and that of Lo- 

 ricata, the former comprising the Tortoises and Turtles, 

 the latter the Crocodiles and their congeners, are natural 

 and well defined ; nor is there any sufficient ground for 

 identifying the latter group with the true Saurians. On 

 the other hand, the Saurians and the Ophidians are so 

 nearly related in all important points of their structure, 

 and pass into each other by such insensible gradations, 

 that I cannot but think that Merrem was correct in view- 

 ing them as constituting a single order, to which he gave 

 the name Squamata, from the nature of their dermal co- 

 vering. If the true Ophidians, or Serpents, be considered 

 as ordinally distinct from the Lizards, the intermediate 

 group to which Mr. Gray has given the name Saurophidia, 

 must also constitute a distinct order ; but I am rather dis- 

 posed to follow Merrem's arrangement. Adding, therefore, 

 the Enaliosaurians of Conybeare, including the great fossil 

 reptiles, the Ichthyosauri and Plesiosauri, as a group 

 probably intermediate between the Tortoises and Croco- 

 diles, we have the following orders of this class ; namely, 

 Testudinata, Enaliosauria, Loricata, and Squamata, the 

 last including the true Saurians, the true Serpents, and 

 the intermediate group, the Saurophidia of Gray. For 

 convenience sake, however, and because the present work 

 is scarcely a fit arena for the discussion of disputed 

 methods of arrangement, I prefer adopting, for the present 

 popular purpose, the more usual one to which I have before 

 alluded. 



