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 /eptiles, the disappearance of the char- 
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Fig. 224.—Tooth of Fig. 225.—Flattened dental plates of a Ray 
Opes obliguus. (Myliobatis Edwardsii). Eocene. 
ocene. 
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” (Hmydide), and by “Soft Tortoises” ( Trionycide). 
The order of the Snakes and Serpents (Of/idia) makes its 
appearance here for the first time under several forms—all of 
ae however, are referable to the non-venomous group of 
the = Constricting Serpents” (ode). The oldest of these 
iS ce Paleophis “toliapicus of the London Clay of Sheppey, 
first made known to science by the researches ot Professor 
Owen. The nearly-allied Paleophis typheus 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 (Paleophis, 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 Monitors 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- 
