nd '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 groups of the Annulosa, the Insecta and the Arachnida,
are represented in the Coal, either by existing genera, or by forms
differing from existing genera in quite minor peculiarities.

Turning to the Vertebrata, the only Paleozoic Elasmobranch Fish of
which we have any complete knowledge is the Devonian and Carboniferous
'Pleuracanthus', which differs no more from existing Sharks than these
do from one another.

Again, vast as is the number of undoubtedly Ganoid fossil Fishes, and
great as is their range in time, a large mass of evidence has recently
been adduced to show that almost all those respecting which we possess
sufficient information, are referable to the same sub-ordinal groups
as the existing 'Lepidosteus', 'Polypterus', and Sturgeon; and that a
singular relation obtains between the older and the younger Fishes;
the former, the Devonian Ganoids, being almost all members of the same
sub-order as 'Polypterus', while the Mesozoic Ganoids are almost
all similarly allied to 'Lepidosteus'.* ([Footnote] *"Memoirs of the
Geological Survey of the United Kingdom.--Decade x. Preliminary Essay
upon the Systematic Arrangement of the Fishes of the Devonian Epoch.")

Again, what can be more remarkable than the singular constancy of
structure preserved throughout a vast period of time by the family
of the Pycnodonts and by that of the true Coelacanths; the former
persisting, with but insignificant modifications, from the Carboniferous
to the Tertiary rocks, inclusive; the latter existing, with still less
change, from the Carboniferous rocks to the Chalk, inclusive?

Among Reptiles, the highest living group, that of the Crocodilia,
is represented, at the early part of the Mesozoic epoch, by species
identical in the essential characters of their organization with those
now living, and differing from the latter only in such matters as the
form of the articular facets of the vertebral centra, in the extent to
which the nasal passages are separated from the cavity of the mouth by
bone, and in the proportions of the limbs.

And even as regards the Mammalia, the scanty remains of Triassic and
Oolitic species afford no fo