It had not been until he had made that first circle that Jason Gridley had realized the handicap that this horizonless landscape of Pellucidar had placed upon his chances of return. He had thought of a mountain standing boldly out against the sky, for such a landmark would have been almost constantly within the range of his vision during the entire flight. There were mountains in the distance, but they stood out against no background of blue sky nor upon any horizon. They simply merged with the landscape beyond them, curving upward in the distance. Twice he circled, his keen eyes searching for any outstanding point in the topography of the country beneath him, but there was nothing that was more apparent than the grassy plain upon which the O-220 rested. He felt that he could not waste time and fuel by searching longer for a landmark that did not exist, and while he realized that the plain would be visible for but a comparatively short distance he was forced to accept it as his sole guide in lieu of a better one. Roaring above the leafy roof of the primeval forest, all that transpired upon the ground below was hidden from him and it was tantalizing to realize that he might have passed directly over the heads of the comrades he sought, yet there was no other way. Returning, he would either circle or hold an exaggerated zig-zag course, watching carefully for sign of a signal. For almost two hours Jason Gridley held a straight course, passing over forest, plain and rolling, hilly country, but nowhere did he see any sign of those he sought. Already he had reached the limit of the distance he had planned upon coming when there loomed ahead of him in the distance a range of lofty mountains. These alone would have determined him to turn back, since his judgment told him that the lost members of the party, should they have chanced to come this far, would by now have realized that they were traveling in the wrong direction. As he banked to turn he caught a glimpse out of the corner of an eye of something in the air above him and looking quickly back, Jason Gridley caught his breath in astonishment. Hovering now, almost above him, was a gigantic creature, the enormous spread of whose wings almost equalled that of the plane he was piloting. The man had a single glimpse of tremendous jaws, armed with mighty teeth, in the very instant that he realized that this mighty anachronism was bent upon attacking him. Gridley was flying at an altitude of about three thousand feet when the huge pteranodon launched itself straight at the ship. Jason sought to elude it by diving. There was a terrific crash, a roar, a splintering of wood and a grinding of metal as the pteranodon swooped down upon its prey and full into the propeller. What happened then, happened so quickly that Jason Gridley could not have reconstructed the scene five seconds later.