tain existing forms. It is only
when we come to the orders, which may be roughly estimated at about a
hundred and thirty, that we meet with fossil animals so distinct from
those now living as to require orders for themselves; and these do not
amount, on the most liberal estimate, to more than about 10 per cent, of
the whole.

There is no certainly known extinct order of Protozoa; there is but one
among the Coelenterata--that of the rugose corals; there is none among
the Mollusca; there are three, the Cystidea, Blastoidea, and
Edrioasterida, among the Echinoderms; and two, the Trilobita and
Eurypterida, among the Crustacea; making altogether five for the great
sub-kingdom of Annulosa. Among Vertebrates there is no ordinally
distinct fossil fish: there is only one extinct order of Amphibia--the
Labyrinthodonts; but there are at least four distinct orders of
Reptilia, viz. the Ichthyosauria, Plesiosauria, Pterosauria, Dinosauria,
and perhaps another or two. There is no known extinct order of Birds,
and no certainly known extinct order of Mammals, the ordinal
distinctness of the "Toxodontia" being doubtful.

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 ordinarily 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
phaenomenon 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.[36] 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