[Illustration: FIG. 121.—_Toxochelys latiremis_; front leg: _hum_, humerus; _rad_, radius; _ul_, ulna; _int_, intermedium; _uln_, ulnare; _p_, pisiform; _cen_, centrale. (From Wieland.)] [Illustration: FIG. 122.—_Desmatochelys lowii_; skull from above and below.] Forty-four years ago the late Professor E. D. Cope, one of the greatest naturalists America has ever produced, in almost the earliest exploration of the great Cretaceous fossil deposits of western Kansas, discovered and collected a remarkable specimen of one of the most extraordinary turtles that is known even yet. By an error somewhat natural for those times, when the theory of evolution was just beginning to attain acceptance by naturalists, he thought that the specimen, notwithstanding its monstrous size, represented a very primitive kind of turtle, and gave to it the name _Protostega gigas_, meaning gigantic first roof! The late Professor George Baur, to whom paleontology owes so much, showed that, far from being a primitive turtle, _Protostega_ was really one of the most specialized types of the order. Professor Cope’s account of the discovery of the specimen is of so much interest that it may be quoted here: “In the very young tortoise or turtle 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 at the end. In the sea-turtles 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. After several square feet of rock had been removed, we cleared up the 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 binder’s board. The edges were fingered and the surface was hard and smooth. All this was quite new, among fully grown animals. 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 the largest species of sea-turtle yet known. But the ribs were those of an ordinary turtle just hatched, and the great plates represented the bony deposit in the skin, which, commencing independently in modern turtles, unite with each other 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