arine fauna of the
Triassic period.

[Illustration: Fig. 140.--_Zamia spiralis_, a living Cycad.
Australia.]

The _plants_ of the Trias are, on the whole, as distinctively
Mesozoic in their aspect as those of the Permian are Palaeozoic.
In spite, therefore, of the great difficulty which is experienced
in effecting a satisfactory stratigraphical separation between
the Permian and the Trias, we have in this fact a proof that the
two formations were divided by an interval of time sufficient
to allow of enormous changes in the terrestrial vegetation of the
world. The _Lepidodendroids, Asterophyllites_, and _Annularioe_,
of the Coal and Permian formations, have now apparently wholly
disappeared: and the Triassic flora consists mainly of Ferns,
Cycads, and Conifers, of which only the two last need special
notice. The _Cycads_ (fig. 140) are true exogenous plants, which
in general form and habit of growth present considerable resemblance
to young Palms, but which in reality are most nearly related to
the Pines and Firs (_Coniferoe_). The trunk is unbranched, often
much shortened, and bears a crown of feathery pinnate fronds.
The leaves are usually "circinate"--they unroll in expanding,
like the fronds of ferns. The seeds are not protected by a
seed-vessel, but are borne upon the edge of altered leaves, or
are carried on the scales of a cone. All the living species of
Cycads are natives of warm countries, such as South America, the
West Indies, Japan, Australia, Southern Asia, and South Africa.
The remains of Cycads, as we have seen, are not known to occur
in the Coal formation, or only to a very limited extent towards
its close; nor are they known with certainty as occurring in
Permian deposits. In the Triassic period, however, the remains
of Cycads belonging to such genera as _Pterophyllum_ (fig. 141,
b), _Zamites_, and _Podozamites_ (fig. 141, c), are sufficiently
abundant to constitute quite a marked feature in the vegetation;
and they continue to be abundantly represented throughout the
whole Mesozoic series. The name "Age of Cycads," as applied to
the Secondary epoch, is therefore, from a botanical point of
view, an extremely appropriate one. The _Conifers_ of the Trias
are not uncommon, the principal form being _Veltzia_ (fig. 141,
a), which possesses some peculiar characters, but would appear
to be most nearly related to the recent Cypresses.

[Illustration: Fig. 141.--Triassic Conifers and Cycads. a, _Voltzia_
(