6 INTRODUCTION 



garded as burrowing types independently derived 

 from some Ophidian form less specialized than any 

 with which we are at present acquainted, and prob- 

 ably without direct relationship to the Lizards, the 

 family Boidae, and more especially the Pythons, 

 claim the position of ancestral group, from which 

 all other snakes may have been derived. 



Viperidas Amblycephalidae 



I 

 Colubridae opisthoglyphae Colubridae proteroglyphae 



Uropeltidas 



I 

 Ilysiidas Xenopeltidae Colubridce aglyphae 



I ! l 



I 



Boidae 



Further remarks on this subject in the chapter 

 on Dentition. 



It is to be regretted that paleontology cannot 

 help us at present as concerns the lines of evolution, 

 the comparatively few fossil Ophidians known, from 

 the Lower Eocene upwards, the remains of which 

 can be identified with some measure of certainty, 

 being either non-poisonous types (Boidce, Ilysiidce, 

 Palceophiidce, Colubvidce) or Viperidce (Viperines from 

 the Miocene of France and Germany, Crotalines from 

 the Miocene of North America). The vertebrae from 

 the Puerco Eocene of America, on the limit between 

 the Cretaceous and Eocene periods, described as the 



