Styx Classics & Edgar Rice Burroughs 
Tarzan and the Jewels of Opar [EPUB ebook] 

Here Tarzan returns to Opar, the source of the gold for lost Atlantis. Ages ago Atlantis sunk beneath the waves — but the denizens of Opar still mine the gold of this lost colony. Tarzan, following greedy pair — one Belgian, one Arab — into the jungle, where they stumble into the lost city. Bad enough — and then Tarzan injures his head in a fight and loses his memory. That's great news for La, the high priestess for the Flaming God, who's had a serious crush on the apeman since their first encounter. But the priests who work for her have other ideas: they don't intend to allow Tarzan to escape their sacrificial knives a second time. . . .