easy to understand; but it is possible that instead of living on hard mail-clad fishes like their toothed cousins of the Lias, their food may have been of a softer nature, such as cuttle-fishes.

In stating that the Fish-Lizards of the Lias subsisted largely on the mail-clad "Ganoid" fishes of the same epoch we may perhaps be thought to be drawing upon our imagination. This, however, is not the case, since we frequently find the whole contents of the stomach of these reptiles preserved within the cavity of their ribs, thereby showing that their food was composed not only of these fishes, but also of young individuals of their own genus. In very rare cases, moreover, there are found within the body-cavity of large individuals very small skeletons of other Fish-Lizards (Fig. 22); and since these young skeletons are always entire and belong to the same species as the one within whose body they are enclosed, it has been concluded that some Fish-Lizards brought forth their young in a living condition. This conclusion is certainly one of the most startling and unexpected results which has rewarded the students of this branch of paleontology.

Whether, when the name of Fish-Lizards was first given to these saurians, it was in the mind of its author that they were really related to fishes, cannot now be certainly known. It has, however, been subsequently suggested that these reptiles are the direct descendants of fishes; but since, like Whales, they breathed air by means of lungs, a recent writer has pointed out that if such descent were really the case it is almost certain

that the Fish-Lizards would have continued to breathe air by means of gills, after the manner of fishes. And it is, therefore, considered probable that these saurians are the descendants of still earlier land reptiles; in which respect they again present another resemblance to Whales, which appear to have been derived from land animals probably more or less nearly allied to the hoofed mammals. If, now, we look back and endeavour to fix upon the ancestral type of creature from which the Fish-Lizards have probably been derived, we are led to select the Primeval Salamanders described in the fourth chapter as the most likely claimants to this position. In treating of that group we have mentioned the peculiar labyrinth-like internal structure of their teeth, from which the name of Labyrinthodonts has been derived. Now it is very suggestive that the teeth of most species of Fish-Lizards retain traces of this very remarkable labyrinthic structure; and since, moreover, the skulls of these saurians have certain peculiar features also found in those of the Labyrinthodonts, while the structure of the backbone is very similar in the two groups, it seems highly probable that the Fish-Lizards have been directly derived from ancient reptiles more or less closely allied to the Labyrinthodonts, if not from that group itself; and that as they gradually became more completely aquatic their limbs were developed into the very complex paddles of the typical forms.

In conclusion, we have already pointed out several remarkable resemblances between the ancient Fish

Lizards and the modern Whales, and have regarded such resemblances as due to their similar mode of life. The Fish-Lizards may, indeed, be considered to have occupied that place in the Secondary period which is now held by the Whales; and it is curious to consider why these saurian devastators of the deep should have died out at the close of the Secondary period, to be succeeded during the Tertiary by the mammalian Whales.

CHAPTER VI.

PLESIOSAURS, OR LONG-NECKED SEA-LIZARDS.

IN the last chapter we gave a description of the remains of those remarkable marine reptiles from the Secondary rocks known as Fish-Lizards, or ShortNecked Sea-Lizards; the general geological relations of the rocks in which their remains occur being there noticed in such a manner that any further allusion to them would be superfluous. The Fish-Lizards were, however, by no means the only reptilian inhabitants of those ancient seas in which the Secondary rocks were deposited. On the contrary, they were accompanied by another group of marine reptiles, equally well adapted for a marine life, but presenting such a totally different type of structure that no one can have any difficulty in distinguishing between the two. So different, indeed, are the skeletons of these two groups of creatures, that with very little instruction every person of ordinary ability ought at once to be able to say to which of the two any single bone he may pick up should be referred. Since the most striking feature in the skeleton of these reptiles, and also one whereby they are very broadly distinguished from the Fish-Lizards, is the great length

of the neck (Fig. 25), they may be conveniently known as Long-Necked Sea-Lizards. Should, however, any of our readers have a fancy for a shorter and more technical term, there is one ready to his hand in the name Plesiosaur. Speaking of the long neck of these reptiles reminds the writer of an answer he received, when examiner at the Calcutta University, from a Bengali, in reply to a question as to the chief points of difference between a Fish-Lizard, or Ichthyosaur, and a Plesiosaur. The misguided student, apparently from having read that portions of the fossilised integuments of the Ichthyosaurs had been obtained, answered the question by stating that Ichthyosaurs were reptiles with a skin, but without a neck, while Plesiosaurs had a neck but no skin.

Like the Fish-Lizards, the Long-Necked Sea-Lizards lived throughout the whole of the Secondary period. Their skeletons, although less common than those of the Fish-Lizards, are preserved in an equally fine state of preservation in the Lias clays of Lyme-Regis and Whitby. Several of the species from the Lias are of comparatively small dimensions, not attaining a length of more than some 8 or 10 feet; but other kinds, more especially those found in the higher Oölitic and Cretaceous rocks, were of enormous dimensions, reaching to a length of 40 feet.

Our earliest knowledge of these strange creatures was mainly derived from the observations of Conybeare and Buckland, made in the earlier decades of the present century. So monstrous and strange did