Second paragraph of third chapter:

“Tarzan will be in full charge of the safari,” said Gregory.

This is a fairly rambling quest story of lost Europeans and sacred jewels in hidden cities (there are actually two of them, not one as implied in the title). I read it because it was published in 1938 and is therefore eligible for the Retro-Hugos; sfnal content is supplied by intelligent apes and an underwater base. Tarzan cares much more about white people than Indians, and more about Indians than apes, and more about apes than Africans, as far as I can tell; there is a telling moment when he and his friends allow a galley to sink with its slaves still chained to the oars, giving it barely a glance. It didn’t get onto my Retro-Hugo nomination list, and won’t get my vote if it is nominated.

Despite all this, it’s a story with an interesting history. It may have seemed familiar to me because it was adapted as the fourth episode of the animated Tarzan, Lord of the Jungle show which I watched as a child. But it originated as an adaptation by Burroughs, in six parts under the title The Red Star of Tarzan, in Argosy earlier in 1938, of a radio story by Rob Thompson, Tarzan and the Diamond of Asher, whose 39 episodes can be found here. It was apparently also used for a newspaper comic strip in early 1938, and adapted for the Tarzan comic in 1970. One of those stories which sums Tarzan up, in any medium.