roamed over the Weald of
Kent, and has left its remains in the Isle of Wight and elsewhere. Such
remains were collected by its discoverer, the late Dr. Mantell, and are
now preserved in our British Museum.

The crocodilia and some of the lizards of our own day are aquatic, but
none live constantly in the ocean, as do the cetacea amongst beasts.
This was, however, by no means always the case. In the secondary period
just adverted to, huge marine reptiles (_Ichthyosauria_ and
_Plesiosauria_) lorded it over the other then inhabitants of the deep,
and presented some noteworthy resemblances to the whales and porpoises
which have since succeeded them.

But other remains preserved in those same secondary rocks show us that
in that period which has been so deservedly called "the age of
reptiles," not only did many huge species of the class stalk over the
land (either browsing on its foliage or preying on their fellows), and
many others swarm in the then existing waters, but it shows us that the
atmosphere also had its reptilian tenants. Flying reptiles which formed
the now extinct order, _Pterosauria_, and which were some of small, some
of very large size, as truly "flew" as do the bats of our own day fly,
and by a very similar mechanism. Moreover, if the _Dinosauria_ present,
as they do present, very noteworthy and interesting resemblances to
birds of the ostrich order, no less noteworthy and interesting are the
resemblances presented by these flying reptiles to ordinary--_i.e._, to
"carinate"--birds.

The orders of extinct reptiles just referred to are not the only ones
which formerly existed and have now passed away. There were reptiles
with peculiarities in their teeth such as to have caused their order to
be named _Amnodontia_, and it is members of this extinct order that the
lizard _Sphenodon_ more or less resembles, and it is this resemblance
which gives it that special interest before noted.

We may now return from these very various extinct forms to enumerate
other kinds of reptiles which exist to-day. But before doing so the fact
may be adverted to, that though amongst beasts many forms have become
extinct, yet the proportion borne by the known extinct forms to the
living kinds is much less than amongst reptiles, and that while it is
the most highly-organized reptiles which have ceased to exist, the
highest mammals which are in any way known to us are those which at
present inhabit the earth's surface.

In pass