vi PREFACE TO THE REPTILIA OF 



Supplement, No. 5, communicated to the Palseontographical Society in the year 1873. 

 A considerable portion of the lower jaw with teeth, transmitted by Mr. Beckles, 

 supplied the ground for determining the side of the crown to which the charac- 

 teristic ridges are limited, that, namely, which is turned toward the cavity of the 

 mouth ; the opposite or outer side of the tooth being smooth. The peculiar shape 

 of the well-preserved symphysial end of the jaw supplied grounds of inference as 

 to the form and movements of the tongue of the great extinct phytophagous or 

 mixed-feeding dragon. Careful display of the tooth-bearing extent of this fossil 

 specimen demonstrated the Reptilian character of the frequent succession and 

 shedding of the teeth — a class-character contrasting with the Mammalian limitation 

 of teeth to two sets, which accordingly bear the designation of the " deciduous " 

 and the " permanent " series ; the first formed, which characterise the immature 

 mammal, being also known as " milk-teeth." 



In 1873 the right ramus, or half of the lower jaw, added acceptable characters 

 of the teeth of the Iguanodon, showing the entire number in the dentary part of 

 the jaw, and the true relative positions of the smooth and the sculptured surfaces 

 of the tooth-crown. This specimen, together with others from other Wealden 

 localities, determined the Reptilian character of a more frequent succession of teeth 

 than in the Mammalian class, a series of larger size being developed to correspond 

 with the increased length of the jaws, and replacing the smaller teeth of the imma- 

 ture periods, which were shed. 



Minor differential characters of the tooth-crown are pointed out, which, if 

 observed only in detached fossil teeth, might have made foundations for distinct 

 species or genera of extinct Reptiles. 



A generic modification of the mandible, previously unnoted, is described 

 as indicative (in addition to, and conformative with, the dental characters) of the 

 vegetable or mixed diet of the great extinct Reptile, which of old once trod what 

 now forms part of the Island of Great Britain. 



Characters of the extinct Reptiles of the same period, indicative of a Dinosaurian 

 family (Prionodontia) by association with the genus Iguanodon, are defined in this 

 Supplement (No. 5), p. 10. The characters of the bony palate, more especially in 

 relation to the position and conformation of the inner or hinder nostrils, are noted 

 in the several Orders of Beptilia, those in the Grocodilia being especially defined. 



Species representative of a genus, but showing a considerable range as to size, 

 are most commonly known in the Mammalian class. A familiar example is mani- 

 fested in the feline genus, where the attempt has been made to add needless com- 

 plexity to zoology by coining a generic name for a small species, distinct from 

 that given by Linnaeus to it as well as to the lion and tiger. But the observed 

 modifications of the dental system are too slight to obtain the suffrages of 

 zoologists for a distinct term. 



