wn to occur in the Keuper
of Germany and in America; and _Paloeosaurus_ (fig. 153. e)
has also been found in the Trias of the same region. Teeth of the
latter, however, are found, along with remains of _Thecodontosaurus_
(fig. 153, d), in a singular magnesian conglomerate near Bristol,
which was originally believed to be of Permian age, but which
appears to be undoubtedly Triassic.

[Illustration: Fig. 152.--Triassic Reptiles. a, Skull of
_Nothosaurus mirabilis_, reduced in size--Muschelkalk, Germany; b,
Tooth of _Simosaurus Gaillardoti_, of the natural size--Muschelkalk,
Germany; c, Tooth of _Beladon Carolinensis_--Trias, America; d,
Tooth of _Thecodontosaurus antiquus_, slightly enlarged--Britain;
e, Tooth of _Paloeosaurus platyodon_, of the natural
size--Britain.]

The Trias has also yielded the remains of the great marine reptiles
which are often spoken of collectively as the "Enaliosaurians"
or "Sea-lizards," and which will be more particularly spoken
of in treating of the Jurassic period, of which they are more
especially characteristic. In all these reptiles the limbs are
flattened out, the digits being enclosed in a continuous skin,
thus forming powerful swimming-paddles, resembling the "flippers"
of the Whales and Dolphins both in their general structure and
in function. The tail is also long, and adapted to act as a
swimming-organ; and there can be no doubt but that these
extraordinary and often colossal reptiles frequented the sea,
and only occasionally came to the land. The Triassic Enaliosaurs
belong to a group of which the later genus _Plesiosaurus_ is
the type (the _Sauropterygia_). One of the best known of the
Triassic genera is _Nothosaurus_ (fig. 152, a), in which the
neck was long and bird-like, the jaws being immensely elongated,
and carrying numerous powerful conical teeth implanted in distinct
sockets. The teeth in _Simosaurus_ (152, b) are of a similar
nature; but the orbits are of enormous size, indicating eyes of
corresponding dimensions, and perhaps pointing to the nocturnal
habits of the animal. In the singular _Placodus_, again, the
teeth are in distinct sockets, but resemble those of many fishes
in being rounded and obtuse (fig. 153), forming broad crushing
plates adapted for the comminution of shell-fish. There is a
row of these teeth all round the upper jaw proper, and a double
series on the palate, but the lower jaw has only a single row of
teeth. _Placodus_ is found in the Muschelka