air) that it swain upon or near the surface; arching back its long neck like the swan, and occasionally darting it down at the fish which happened to float within its reach? It may, perhaps, have lurked in shoal-water along the coast, concealed among the seaweed; and, raising its nostrils to a level with the surface from a considerable depth, may have found a secure retreat from the assaults of dangerous enemies; while the length and flexibility of its neck may have compensated for the want of strength in its jaws, and its incapacity for swift motion through the water, by the suddenness and agility of the attack which they enabled it to make on every animal fitted for its prey which came within its reach."

Nothing that has been discovered since the date when the above passage was penned can suggest any more probable interpretation of the habits of these creatures.

The larger species found in the Lias attained a length of about 20 feet; but, as is so generally the case, we find the size of the species gradually increasing as we ascend in the geological scale, the culmination being reached in the period of the chalk, when, both in Europe and North America, we meet with species reaching to the enormous length of 40 feet, and the joints of whose backbone measured as much as 6 inches in diameter. These terrible creatures must indeed have been dragons of the deep, with a far more strange appearance than any of those imagined in fable.

The general dimensions, although perhaps not the absolute length, of these monsters were, however, greatly exceeded by those of a closely allied group of marine reptiles whose remains occur in the Oxford and Kimeridge clays of the great Oölitic series of rocks. These creatures, which are known by the name of Pliosaurs, although agreeing with the Long-Necked Lizards in the structure of their paddles and backbone, differ very widely from them in having enormous heads, for the support of which a short and thick neck is, of course, absolutely essential. A skull of one of these giants found on the Dorsetshire coast and exhibited in the Natural History Museum, is nearly 6 feet in length; while a hind paddle in the Dorset Museum measures upwards of 6 feet, of which no less than 37 inches is taken up by the thigh-bone alone. The cnormous biting power and destructive habits of these creatures is evidenced by their teeth, which are not unfrequently found in the Kimeridge clay, and one specimen of which is upwards of a foot in length from the tip of the crown to the base of the root. These teeth are readily distinguished from those of all other reptiles, not only by their huge size, but also by the triangular form assumed by their crowns; one surface of the triangle being usually nearly smooth, while the other two are ornamented with vertical ridges.

We may pretty safely assume that in the ancient seas of the Oölitic period the Pliosaurs acted the same part as is played by the ferocious Grampuses in those of the present day.

G

Turning from these latest modifications into which the Long-Necked Lizards were finally developed, and looking back at the earliest known representatives of the group, we find in the strata lying below the Lias, and thus forming the very base of the Secondary rockseries, the remains of a number of more or less closely allied forms, the largest of which did not exceed a yard in length. These small reptiles were evidently ancestral types of the larger species found in the Lias, but they exhibit certain structural features clearly indicating that they were in great part of terrestrial or fresh-water habits, and their whole organisation departs less widely from the general reptilian type than is the case with their successors in time. Thus we reach the conclusion that the Long-Necked Lizards, like the Fish-Lizards, were in all probability descended from small land reptiles, and have been gradually more and more modified for the exigencies of a purely marine life. In this respect, therefore, these ancient creatures present a precise analogy to the Whales and Porpoises of to-day.

CHAPTER VII.

TORTOISES AND TURTLES.

To many of us, the chief idea connected with turtles is that they are used to make turtle-soup; while in regard to tortoises our acquaintance is often limited. to seeing a barrow-load of unfortunate specimens hawked about the streets, or to an individual or two kept in our own or a friend's garden, as a very unsociable kind of pet. We are also acquainted with these creatures by means of tortoise-shell, either in the form of combs or various ornamental articles; although the exact nature of this commodity-which, by the way, comes from turtles and not from tortoises -is frequently but very imperfectly known. Many people, indeed, have more or less hazy ideas as to what kind of animals tortoises and turtles really are. Thus, according to Punch, railway companies were wont to classify tortoises as insects; and the writer well recollects that during his undergraduate days his landlady purchased an unfortunate tortoise to take the place of a deceased hedgehog in the kitchen, for the purpose of eating black-beetles, and was immensely astonished when told that the tortoise was a vegetable feeder and had no sort of kinship with the hedgehog.

Tortoises and turtles, or, as it is frequently convenient to call them, Chelonians (from the Greek name of one species), are, however, in reality a very remarkable group, or order, of the great class of Reptiles; and their structure is so peculiar and interesting that a short glance at some of their chief features cannot fail to be instructive. We are, indeed, accustomed to regard many extinct groups of reptiles, like the FishLizards,* as more bizarre and strange than any which now inhabit the globe; but if we were to be made acquainted for the first time with tortoises from their fossil remains, we should certainly consider them as far more extraordinary than any other types; and it is highly probable that the paleontologist who first made known such a remarkable type of reptilian structure would be charged with having created a totally impossible monster.

The most striking and peculiar feature about tortoises and turtles is the more or less complete bony shell with which their body is protected, on account of which they are noticed in the chapter on "Mail-Clad Animals." The accompanying woodcut (Fig. 27) exhibits a typical Chelonian, as exemplified by a landtortoise. In this creature we see a fully developed bony shell, within which the head, limbs, and tail can be retracted, so as to afford a perfect protection for the entire animal. We have said that the shell of the tortoise is a bony one; but it will probably be at once objected that the "tortoise-shell" of commerce is about *See Chapter V.