It is hardly possible yet to decide whether or not the plesiosaurs were denizens of the open oceans for the most part, far from land. That many of them were rovers is quite certain. With the skeleton of a large plesiosaur found some years ago in western Kansas, there were many siliceous pebbles which could have come only from the shores of the old Cretaceous seas about the Black Hills, hundreds of miles distant. Some of the pebbles are red quartzite, quite identical with that of the bowlders brought to Kansas millions of years later by the glacial drift from outcroppings near the northern line of Iowa. The bones of plesiosaurs are often found in deposits believed to be of deep-water origin. But they are also found in Kansas associated with the remains of small turtles, flying reptiles, and birds which could only have lived near the shores. Indeed, their remains have often been found with those of strictly fresh-water animals which had been brought down by the floods to the seas. Their wide but rather sparse distribution in all kinds of marine sediments would rather indicate that they were at home far out in the tempestuous ocean or near the shores in protected bays, though probably they preferred the shallow water littoral regions. One conclusion is quite justified: they were not gregarious, as were the ichthyosaurs. It is not certain that the plesiosaurs were viviparous, though there are good reasons for the belief that they were. Remains of two embryos were found years ago in England associated in such a way that it is reasonable to suppose they were unhatched young, though embryos have never yet been found associated with skeletons of adults, as have those of ichthyosaurs in numerous instances. Bones of young, often quite young, plesiosaurs, are frequently found in shallow water deposits, and if the young were actually born alive they must have swum freely in the open waters while yet of very tender age. Rather singularly, however, the remains of these young plesiosaurs always occur as isolated bones.