Viperidæ Amblycephalidæ | | Colubridæ opisthoglyphæ Colubridæ proteroglyphæ | | | | +---------------------------+-----+--------------+ | Uropeltidæ | | | Ilysiidæ Xenopeltidæ Colubridæ aglyphæ | | | +------------+--------------+ | Boidæ 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 (_Boidæ_, _Ilysiidæ_, _Palæophiidæ_, _Colubridæ_) or _Viperidæ_ (Viperines from the Miocene of France and Germany, Crotalines from the Miocene of North America). The vertebræ from the Puerco Eocene of America, on the limit between the Cretaceous and Eocene periods, described as the oldest snake remains, _Helagras_, Cope, are stated to approach the Lacertilian type. Whether the vertebræ named _Symoliophis_, Sauvage, from the chalk of France, and _Coniophis_, Marsh, from the Laramie Cretaceous of North America, are Ophidian, as claimed by their describers, or Dolichosaurian, cannot be decided without further material. CHAPTER II EXTERNAL CHARACTERS--INTEGUMENT