1 146 CLASS REPTILIA. 



The very imperfectly known Cetartkrosaurus, of the Cambridge 

 Greensand, which Mr Hulke refers to this order, is noticed among 

 the Ichthyopterygia. 



Suborder 5. Ophidia. — The Serpents and Snakes constituting the 

 last division of the Squamata present the following distinctive fea- 

 tures : The body is greatly elongated (fig. 105 1, bis\ and the vertebral 

 column divisible only into a trunk and a caudal region. The alis- 

 phenoidal region of the skull is fully ossified ; there is no temporal 

 arcade, parietal foramen, or columella ; the quadrate and the bones 

 of the palatal and maxillary regions are loosely attached to the skull 

 (fig. 1049); the premaxillae are more or less aborted and usually 

 edentulous ; and the two rami of the mandible are connected only 

 by ligament. The vertebrae (fig. 1050) have zygosphenes ; but there 

 is no sacrum, and chevrons are also wanting. There is, moreover, 

 no sternum, nor any trace of the pectoral girdle or limbs ; but in 



some cases there are rudiments 

 of the pelvic girdle and limbs. 

 Dermal scutes are invariably 

 wanting. This suborder is di- 

 vided into three sections ; but 

 since its palaeontological history 

 is but imperfectly known, only 

 Fig. io5o.-Posterior (a) and haemal (b) views very brief mention will be made 



of a trunk vertebra of Fytkon molurus I from J 



the Pleistocene of India. of those families represented in 



a fossil state. With the excep- 

 tion of an imperfectly known form from the Chalk, described under 

 the name of Cimoliophis, all the known fossil forms are of Tertiary 

 or Post-tertiary age. The next earliest genus is Helagrus, of the 

 Lowest (Puerco) Eocene of North America, in which the imperfect 

 development of the zygantrum of the vertebrae indicates very gener- 

 alised affinities. 



Family Colubrid^e. — The first existing family of the section 

 Colubriformes, or Innocuous Snakes, contains the great bulk of the 

 suborder ; and, with the exception of Australia, is represented in 

 nearly all temperate and warm regions. The Indian genus Ptyas 

 is probably represented in the Pleistocene of Madras by the existing 

 P. mucosus. In the Middle Miocene of France we have the extinct 

 Pilemophis closely related to the modern Tropidonotus, or common 

 English Snake ; while the existing genus Elaphis occurs in the 

 Upper and Lower Miocene of various parts of the Continent. A 

 species of Periops closely allied to one now living in Egypt occurs 

 in the Pleistocene of Coudes, in the south of France ; and Tham- 

 nophis, from the Middle Miocene of the latter country, is said to be 

 allied to Elaphis. 



Family PYTHONiDiE. — The Pythons, or Rock Snakes, are now 



