Adventure Comics #314

The villainous Alaktor steals a Legion Time Bubble, rescues Emperor Nero, John Dillinger, and Adolf Hitler from the past, and transfers their minds into the bodies of Mon-El, Ultra Boy, and Superboy. First appearance of Legion reject Ron-Karr (of Neptune, spelled "Ronn Kar" in this story) of Neptune and of the Lost World, an ancient planet capable of traveling through space by means of an enormous rocket engine.