Jana had thrown herself prone among the grasses and was urging Tarzan to do likewise. Crouching low, his eyes just above the grasses, Tarzan watched the huge dinosaur. "I think he has caught our scent," he said. "He is standing with his head up, looking about him; now he is trotting around in a circle. He is very light on his feet for a beast of such enormous size. There, he has caught a scent, but it is not ours; the wind is not in the right direction. There is something approaching from our left, but it is still at a considerable distance. I can just hear it, a faint suggestion of something moving. The Gyor is looking in that direction now. Whatever is coming is coming swiftly. I can tell by the rapidly increasing volume of sound, and there are more than one--there are many. He is moving forward now to investigate, but he will pass at a considerable distance to our left." Tarzan watched the Gyor and listened to the sound coming from the, as yet, invisible creatures that were approaching. "Whatever is approaching is coming along the bottom of the ravine we just crossed," he whispered. "They will pass directly behind us." Jana remained hiding low in the grasses. She did not wish to tempt Fate by revealing even the top of her head to attract the attention of the Gyor. "Perhaps we had better try to crawl away while his attention is attracted elsewhere," she suggested. "They are coming out of the ravine," whispered Tarzan. "They are coming up over the edge--a number of men--but in the name of God what is it that they are riding?" Jana raised her eyes above the level of the grasses and looked in the direction that Tarzan was gazing. She shuddered. "They are not men," she said; "they are the Horibs and the things upon the backs of which they ride are Gorobors. If they see us we are lost. Nothing in the world can escape the Gorobors, for there is nothing in all Pellucidar so swift as they. Lie still. Our only chance is that they may not discover us." At sight of the Horibs the Gyor emitted a terrific bellow that shook the ground and, lowering his head, he charged straight for them. Fully fifty of the Horibs on their horrid mounts had emerged from the ravine. Tarzan could see that the riders were armed with long lances--pitiful and inadequate weapons, he thought, with which to face an enraged triceratop. But it soon became apparent that the Horibs did not intend to meet that charge head-on. Wheeling to their right they formed in single file behind their leader and then for the first time Tarzan had an exhibition of the phenomenal speed of the huge lizards upon which they were mounted, which is comparable only to the lightning-like rapidity of a tiny desert lizard known as a swift.