The positive change in passing from the recent to the ancient animal
world is greater, but still singularly small. No fossil animal is so
distinct from those now living as to require to be arranged even in a
separate class from those which contain 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 ordinally distinct from those now living; while the far less