.

The objection that broad statements of this kind, after all, rest largely
on negative evidence is obvious, but it has less force than may at first
be supposed; for, as might be expected from the circumstances of the
case, we possess more abundant positive evidence regarding Fishes and
marine Mollusks than respecting any other forms of animal life; and yet
these offer us, through the whole range of geological time, no species
ordinally distinct from those now living; while the far less numerous
class of Echinoderms presents three, and the Crustacea two, such orders,
though none of these come down later than the Palaeozoic age. Lastly, the
Reptilia present the extraordinary and exceptional phenomenon of as many
extinct as existing orders, if not more; the four mentioned maintaining
their existence from the Lias to the Chalk inclusive.

Some years ago one of your Secretaries pointed out another kind of
positive palaeontological evidence tending towards the same conclusion--
afforded by the existence of what he termed "persistent types" of
vegetable and of animal life.[4] He stated, on the authority of Dr.
Hooker, that there are Carboniferous plants which appear to be
generically identical with some now living; that the cone of the Oolitic
_Araucaria_ is hardly distinguishable from that of an existing species;
that a true _Pinus_ appears in the Purbecks and a _Juglans_ in the Chalk;
while, from the Bagshot Sands, a _Banksia_, the wood of which is not
distinguishable from that of species now living in Australia, had been
obtained.

[Footnote 4: See the abstract of a Lecture "On the Persistent Types of
Animal Life," in the _Notices of the Meetings of the Royal Institution of
Great Britain_.--June 3, 1859, vol. iii. p. 151.]

Turning to the animal kingdom, he affirmed the tabulate corals of the
Silurian rocks to be wonderfully like those which now exist; while even
the families of the Aporosa were all represented in the older Mesozoic
rocks.

Among the Mollusca similar facts were adduced. Let it be borne in mind
that _Avicula, Mytilus, Chiton, Natica, Patella, Trochus, Discina,
Orbicula, Lingula, Rhynchonclla_, and _Nautilus_, all of which are
existing _genera_, are given without a doubt as Silurian in the last
edition of "Siluria"; while the highest forms of the highest Cephalopods
are represented in the Lias by a genus _Belemnoteuthis_, which presents
the closest relation to the existing _Loligo_.

The two highest