roduction of new forms. The Ichthyosaurs, the Plesiosaurs,
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 "Terrapins" (_Emydidoe_), and by "Soft Tortoises"
(_Trionycidoe_). The order of the Snakes and Serpents (_Ophidia_)
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" (_Boidoe_). The oldest of
these is the _Paloeophis toliapicus_ of the London Clay of Sheppey,
first made known to science by the researches of Professor Owen.
The nearly-allied _Paloeophis typhoeus_ 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
(_Paloeophis, 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-west of England, there occur fossil
remains of all the three living types of Crocodilians--namely, the
Gavials, the true Crocodiles, and the Alligators (fig. 226)--though
at the present day these forms are all geographically restricted
in their range, and are never associated together.

[Illustration: Fig. 226.--Upper jaw of Alligator. Eocene Tertiary,
Isle of Wight.]

Almost all the existing orders of _Birds_, if not all, are
represented in the Eocene deposits by remains often very closely
allied to existing types. Thus, amongst the Swimming Birds
(_Natatores_) we find examples of forms allied to the living
Pelicans and Mergansers; amongst the Waders (_Grallatores_) we
have birds resembling the Ibis (the _Numenius gypsorum_ of the
Paris basin); amongst the Running Bir