In our illustration, Plate XIII., the artist has represented the Elasmosaurus[37] (of Cope) with its long thin neck stretched out in search of food on the bed of the sea. Professor Cope--thus describing this monster, in language which seems somewhat fanciful--says, "Far out on the expanse of this ancient sea might have been seen a huge snake-like form, which rose above the surface, and stood erect, with tapering throat and arrow-shaped head, or swayed about, describing a circle of twenty feet radius above the water. Then plunging into the depths, naught would be visible but the foam caused by the disappearing mass of life. Should several have appeared together, we can easily imagine tall, flexible forms rising to the height of the masts of a fishing-fleet, or like snakes twisting and knotting themselves together. This extraordinary neck--for such it was--rose from a body of elephantine proportions. The limbs were probably two pairs of paddles, like those of Plesiosaurus, from which this diver chiefly differed in the arrangement of the bones of the breast. In the best-known species twenty-two feet represent the neck in a total length of fifty feet. This is Elasmosaurus platyurus (Cope), a carnivorous sea-reptile, no doubt adapted for deeper waters than many of the others. Like the snake-bird of Florida, it probably often swam many feet below the surface, raising the head to the distant air for breath, then withdrawing it, and exploring the depths forty feet below, without altering the position of its body. From the localities in which the bones have been found in Kansas, it must have wandered far from land; and that many kinds of fishes formed its food is shown by the teeth and scales found in the position of its stomach." [37] Greek--_elasmos_, plate; _sauros_, lizard: probably on account of the shape of the paddles. But to return to the sea-serpents. Mosasaurus is now known to have been a long slender reptile, with a pair of powerful paddles in front, a moderately long neck, and flat pointed head. The tail was very long--flat and deep--like that of a great eel. Mosasaurus princeps is computed to have been seventy-five to eighty feet long. Clidastes was another genus of long and slender shape, one species of which reached a length of forty feet. Some forms of sea-serpent had sclerotic plates in the eye, such as we found in the fish-lizard, or Ichthyosaurus (p. 46), but the announcement that their bodies were protected by bony plates has turned out to be a mistake, and the supposed plates really belonged to the eye. Leiodon proriger (Cope) was abundant in the old North American Cretaceous sea, and reached a length of seventy-five feet. It had a long projecting muzzle, somewhat like the snout of a sturgeon. Platecarpus and Tylosaurus had peculiarly sharp-pointed heads (see Fig. 40). [Illustration: Fig. 40.--Snout of Tylosaurus. (After Marsh.)]