Tortoises were the boatmen of the cretaceous waters of the eastern coast, but none had been known from the deposits of Kansas until very recently. One species now on record (_Protostega gigas_, Cope), is of large size, and strange enough to excite the attention of naturalists. It is well known that the house or boat of the tortoise or turtle is formed by the expansion of the usual bones of the skeleton till they meet and unite, and thus become continuous. Thus the lower shell is formed of united ribs of the breast and breast-bone, with bone deposited in the skin. In the same way the roof is formed by the union of the ribs with bone deposited in the skin. In the very young tortoise the ribs are separate as in other animals; as they grow older they begin to expand at the upper side of the upper end, and, with increased age, the expansion extends throughout the length. The ribs first come in contact where the process commences, and in the land-tortoise they are united to the end. In the sea-turtle, the union ceases a little above the ends. The fragments of the _Protostega_ were seen by one of the men projecting from a ledge of a low bluff. Their thinness and the distance to which they were traced excited my curiosity, and I straightway attacked the bank with the pick. After several square feet of rock had been removed, we cleared up one floor, and found ourselves well repaid. Many long slender pieces, of two inches in width, lay upon the ledge. They were evidently ribs, with the usual heads, but behind each head was a plate like the flattened bowl of a huge spoon placed crosswise. Beneath these stretched two broad plates two feet in width, and no thicker than binders' board. The edges were fingered, and the surface hard and smooth. All this was quite new among fully grown animals, and we at once determined that more ground must be explored, for further light. After picking away the bank and carving the soft rock, new masses of strange bones were disclosed. Some bones of a large paddle were recognized, and a leg bone. The shoulder-blade of a huge tortoise came next, and further examination showed that we had stumbled on the burial-place of one of the largest species of sea-turtle yet known. The single bones of the paddle were eight inches long, giving the spread of the expanded flippers as considerably over twenty feet. But the ribs were those of an ordinary turtle just born, and the great plates represented the bony deposit in the skin, which, commencing independently in modern turtles, united with the expanded ribs below, at an early day. But it was incredible that the largest of known turtles should be but just hatched, and for this and other reasons it has been concluded that this "ancient mariner" is one of those forms not uncommon in old days, whose incompleteness in some respects points to the truth of the belief, that animals have assumed their modern perfection, by a process of growth from more simple beginnings.