“Yes, yes, he is right, Mr. Round-up Dick,” he answered. “The Indians did not have horses before the white man came. You will remember that even among the Sioux, all their early means of transport was with a dog travois, two poles dragging along the ground. When the Sioux did get horses, they merely made a longer travois.” “What killed off all the horses?” “It’s a mystery,” Perry answered, “no one really knows. We’ve found fossils of insects like the tse-tse fly—that’s the one that causes sleeping-sickness among the cattle in Africa—and maybe there was a plague of these flies which started an epidemic that killed off all the wild horses.” Perry was about to plunge into a talk over the different reasons why some of the older types of animals became extinct, when suddenly, the cowboy gave a whoop and spurred his horse to the gallop. As they were riding down a gully, where the ground was very uneven, the boy was only too glad to pay full attention to his mount. But the cow pony, though going at full speed, picked his way perfectly. In full career, Round-up Dick swerved round the corner of a cliff and stopped dead. Perry had just time to brace himself against being thrown over his pony’s head, when the cowboy, pointing with his finger, said: “Give it a handle!” Perry looked up. There, standing out from the cliff as though it were one of the ancient bulls of Assyria, was part of the skull and the foot of an animal, the hoof pointed downwards as though the creature were going to gallop right out of the cliff. Perry slapped his pony’s neck in the exuberance of his delight and had a few moments of unexpected war-dance. “Antoine! Antoine!” he cried, clinging to the saddle as best he could, “do you see it?” As the young paleontologist had been looking at the fossil steadily all the time that the lad’s pony was prancing around on its hind legs, the question was quite unnecessary, but the boy had to blow off steam. “It is a Mesohippus!” he cried excitedly, “it is, it is, it is!” Antoine shook his head. “It is a Hyrachyus,” he said. Then, turning to the cowboy, he continued, “this is the three-toed rhinoceros that I told you about, Mr. Round-up Dick. And,” he added, his eyes kindling, “it may be a perfect specimen.” “A Hyrachyus!” chanted the boy. “Gee! What a find!” The cowboy shifted impatiently in his saddle. “Let’s see the color o’ the cards,” he said. Antoine shook his feet free of the stirrups, and with an ease that surprised the boy, raised himself to his feet on the saddle. Standing, the Belgian could just see into the jaw of the skull. He examined the teeth carefully, then looked down at the two eager questioners.