Tarzan: The Epic Adventures — R.A. Salvatore

Russian exile Nikolas Rokoff has stolen an ancient crystal amulet--the key to terrifying power. It can be used to conquer the very depths of time and space, but if Rokoff releases its supernatural forces, the gem will rip apart the fabric of reality. He will throw open the gates to Pellucidar--the prehistoric land at the Earth's core. In doing so, he will unleash the grotesque, reptilian armies of the Mahars.
Only Tarzan, Lord of the Jungle, can hope to stop the flood of creatures whose one goal is bloodthirsty conquest. But even Tarzan may fall prey to the talons of Mora, the ruthless and seductive Queen of the Mahars.
STARRING THE LEGENDARY HERO CREATED BY EDGAR RICE BURROUGHS