pointed, “with trenchant and finely serrate margins” (Owen).  The bodies of the vertebrae are hollowed out at both ends, but the limbs appear to be adapted for progression on the land.  The genus Belodon (fig. 152, c) is known 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 Muschelkalk, and the characters of its dental apparatus indicate that it was much more peaceful in its habits than its associates the Nothosaur and Simosaur.

[Illustration:  Fig. 153.—­Under surface of the upper jaw and palate of Placodus gigas.  Muschelkalk, Germany.]