296 HISTORICAL PALAEONTOLOGY. 



teeth of Rays (fig. 225), consisting of flat bony pieces placed 

 close together, and forming " a kind of mosaic pavement on 

 both the upper and lower jaws " (Owen). 



In the class of the Reptiles, the disappearance of the char- 



Fig. 224.— Tooth of Fig. 225.— Flattened dental plates of a Ray 



Oiodus obliqtms. {Myliobatis Edwardsii). Eocene. 



Eocene. 



acteristic Mesozoic types is as marked a phenomenon as the 

 introduction of new forms. The Ichthyosaurs, the Plesio- 

 saurs, the Pterosaurs, and the Mosasaurs of the Mesozoic, 

 find no representatives in the Eocene Tertiary; and the same 

 is true of the Deinosaurs, if we except a few remains from the 

 doubtfully-situated " Lignitic formation " of the United States. 

 On the other hand, all the modern orders of Reptiles are 

 known to have existed during the Eocene period. The 

 Chelonians are represented by true marine Turtles, by " Ter- 

 rapins" {Einydidce), and by "Soft Tortoises" {Trw?iyddcB). 

 The order of the Snakes and Serpents {Op/iidia) makes its 

 appearance here for the first time under several forms — all of 

 which, however, are referable to the non-venomous group of 

 the " Constricting Serpents " {Boidce). The oldest of these 

 is the PalfBophis toliapicus of the London Clay of Sheppey, 

 first made known to science by the researches of Professor 

 Owen. The nearly - allied Palceophis typhmis of the Eocene 

 beds of Bracklesham appears to have been a Boa-constrictor- 

 like Snake of about twenty feet in length. Similar Python- 

 like Snakes {Falceophis, Dinophis, &c.) have been described 

 from the Eocene deposits of the United States. True Lizards 

 {Lacertilians) are found in some abundance in the Eocene 

 deposits, — some being small terrestrial forms, like the common 

 European lizards of the present day ; whilst others equal or 

 exceed the living INIonitors in size. Lastly, the modern order 

 of the Crocodilia is largely represented in Eocene times, by 

 species belonging to all the existing genera, together with 

 others referable to extinct types. As pointed out by Owen, 

 it is an interesting fact that in the Eocene rocks of the south- 



