hideous, and always grotesque creatures. Let us consider for a little some of the more conspicuous forms, referring to our illustration for their portraits. Every text-book figures the well-known types of the genera _Ichthyosaurus_ and _Plesiosaurus_; we need scarcely, therefore, dwell on them, except to state that the catalogues of British fossils include eleven species of the former genus and eighteen of the latter, We may, however, notice some of the less familiar points of comparison of the two genera. Both were aquatic, and probably marine. Both swam by means of paddles; both were carnivorous, and probably fed principally upon fishes; both were proper reptiles, and breathed air, and had large and capacious lungs. Yet with these points in common, no two animals could have been more different in detail. The Ichthyosaurus had an enormous head, with powerful jaws, furnished with numerous and strong teeth. Its great eyes, strengthened by a circle of bony plates, exceeded in dimensions, and probably in power of vision under water, those of any other animal, recent or fossil. Its neck was short, its trunk massive, with paddles or swimming limbs of comparatively small size, and a long tail, probably furnished with a caudal fin or paddle for propulsion through the water. The Plesiosaur, on the other hand, had a small and delicate head, with slender teeth and small eyes. Its neck, of great length and with numerous joints, resembled the body of a serpent. Its trunk, short, compact, and inflexible, was furnished with large and strong paddles, and its tail was too short to be of any service except for steering. Compared with the Ichthyosaur, it was what the giraffe is to the rhinoceros, or the swan to the porpoise. Two fishermen so variously and differently fitted for their work it would be difficult to imagine. But these differences were obviously related to corresponding differences in food and habit. The Ichthyosaur was fitted to struggle with the waves of the stormy sea, to roll therein like modern whales and grampuses, to seize and devour great fishes, and to dive for them into the depths; and its great armour-plated eyes must have been well adapted for vision in the deeper waters. The Plesiosaur, on the contrary, was fitted for comparatively still and shallow waters; swimming near the surface with its graceful neck curving aloft, it could dart at the smaller fishes on the surface, or stretch its long neck downward in search of those near the bottom. The Ichthyosaurs rolled like porpoises in the surf of the Liassic coral reefs and the waves beyond; the Plesiosaurs careered gracefully in the quiet waters within. Both had their beginning at the same time in the earlier Mesozoic, and both found a common and final grave in its later sediments. Some of the species were of very moderate size, but there were Ichthyosaurs twenty five feet long, and Plesiosaurs at least eighteen feet in length.