is chiefly effected by the tail, the humeri and femora, the upper arm and thigh bones were elongated, and not shortened. They form the rigid and stout handles of oars whose blades are the thinner, flexible forearm, wrist, and fingers, or the corresponding foreleg, ankle, and toes. No other purely aquatic reptiles, save the turtles, which likewise are of the oar-propelled type, have elongated arm and thigh bones. Textbook illustrations of the plesiosaurs usually depict the necks, like those of the swans, freely curved, and a popular scientific article in one of our chief magazines a few years ago depicted one of them with the neck coiled like the body of a snake. One noted paleontologist, indeed, not many years ago described the plesiosaurs as resting on the bottom in shallow waters with the neck uplifted above the surface viewing the waterscape! And when we consider the fact that some species of the elasmosaurs had a neck not less than twenty feet in length, such a flexible use of it would not seem improbable. But the plesiosaurs did not and could not use the neck in such ways. They swam with the neck and head, however long, directed in front, and freedom of movement was restricted almost wholly to the anterior part. The posterior part of the neck was thick and heavy, and could not have been moved upward or downward to any considerable extent and not very much laterally. From all of which it seems evident that the plesiosaurs caught their prey by downward and lateral motions of their neck, rather than by quick swimming. [Illustration: FIG. 43.—Gastroliths and bones of an undetermined plesiosaur from the Lower Cretaceous of Kansas.]