REPTILE GALLERY. 



Fief. 1. 



Back view of skull of Crocodile. 

 o, single occipital condyle : q, quadrate bone. 



type, of which only one representative is still living (in New Zealand). 

 Reptiles flourished and attained their greatest development in the 

 Secondary period — Pterosaurians (large flying Lizards, see Geolo- 

 gical Guide, p. 39), Dinosaurians (huge terrestrial Reptiles far 

 exceeding in size our largest Crocodiles), Dicynodonts, Ichthyosau- 

 rians, and Plesiosaurians (large marine creatures, Geological Guide, 

 pp. 41, 45, 47), Crocodiles, Lizards, and Turtles lived in abun- 

 dance; Snakes, however, did not appear before the Tertiary period. 

 At present some 4000 species of Reptiles are known, which are 

 unequally divided among five Orders, viz. Crocodilia (Crocodiles 

 and Alligators), Rhynchocephalia, Lacertilia (Lizards), Ophidia 

 (Snakes), and Chelonia (Tortoises and Turtles). 



In this classification of Reptiles the naturalist is guided much 

 more by the structure of the skeleton and the other internal organs 

 than by the external appearance. In fact, in Reptiles, as in many 

 other classes of the Animal Kingdom, outward similarity is decep- 

 tive as to the natural relationship — that is, as to the degree in 

 which they are related to each other as descendants from a more or 

 less remote common ancestor. Take, for instance, a Crocodile, a 

 Lizard, a Slowworm, and a Snake. The observer who, like the 



