Page:A Treatise on Geology, volume 1.djvu/109

 CH. V., hylseosaurus, and iguanodon. They occur in the oolitic and wealden deposits. Of the lacertilia we have seven genera,—viz. mososaurus, leiodon, raphiosaurus, lacerta; rhynchosaurus, thecodontosaurus, palæosaurus, and cladyodon. Of the ten species of these genera, five have been discovered in the new red sandstone series, one in the oolite, three in the chalk, and one in the crag. Of the pterosauria three species are known in the lias, oolite, and chalk.

Finally. Polyptychodon from the lower greensand, and rysosteus from the bone bed of Aust, are not yet referred to their proper sub-order.

Among the singularities revealed by these investigations, we may notice in the ichthyosaurus the curious and beautiful combination of the swimming form and retral nostrils of the dolphin; the teeth of the gavial, or crocodile; paddles somewhat like those of the turtle; vertebrae like those of a fish; and eyes furnished with sclerotic bones like those of birds and certain lizards.

The iguanodon and megalosaurus have the "immania membra " requisite to sustain their vast bulk on land; but pterodactylus, an almost fabulous creation, unites the wings of a bat with the skeleton of a lizard; its long neck being formed of only seven vertebrae; while the snake-like neck of plesiosaurus includes from thirty to forty.

In magnitude some of these fossil reptiles surpass the largest crocodiles. The iguanodon—not the largest of the wealden saurians—may have measured forty or fifty feet in length: the batrachian of the new red must have been something like a toad three or four feet long, and the largest pterodactyl of the chalk may have extended sixteen feet and a half between the tips of the wings.

The existing crocodiles offer in the saurian group a particular and distinct type, which seems to unite, in some degree, the characters of the chelonida and true