ts; 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
numerous class of Echinoderms presents three; and the Crustacea two,
such orders, though none of these come down later than the Paleozoic
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 paleontologic evidence tending towards the same
conclusion--afforded by the existence of what he termed "persistent
types" of vegetable and of animal life.* ([Footnote] *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.) 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.

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 Molluska similar facts were adduced. Let it be borne in mind
that 'Avicula', 'Mytalis', 'Chiton', 'Natica', 'Patella', 'Trochus',
'Discina', 'Orbicula', 'Lingula', 'Rhynchonella', a