Well, KA, you've inspired yet another afternoon of enlightening research. I've read ERB's
The Moon Maid, and done quite a bit of research today on Lovecraft, a writer I've previously avoided due to his low opinion of my direct ancestors, among others.
And now I think we can reconcile all this:
1. In ERB's
The Moon Maid, the action takes place in 2016; our story takes place over a hundred years earlier, so we can play with it. One possible scenario: The U-ga are descendants/ancestors of the Vril-ya, who live deep within the moon in the 19th century. A clue to this is that Nah-ee-lah is first seen in the novel flying on wings, which are torn from her when she is captured. We could create a backstory (or front story) that asserts that the Vril-ya (or U-ga in their own language; there
is a similarity in the names) do not leave the moon until
after they make contact with earthmen in the time that our story covers. They will later come to earth and make contact with the Chthuli, and colonize their underground world. They will bring some of the Chthuli back home to the moon with them, and those creatures will become the Kalkar and Lu-thans, among other beastial moon races, that Julian 9 discovers in 2016, who will eventually overthrow the U-ga and attack earth.
That this doesn't fit with the histories of the Chthuli as related in Lovecraft's books is explained by Lovecraft himself: they lie, often, about their own origins in order to build themselves up.
2. That the ancient inhabitants of Atlantis would have made sacrifices to the
underground Chthonic races fits perfectly with our map, as they are directly under Atlantis, Mu and Lemuria on our map. They would control two resources, Vrill (which will eventually attract the U-ga to earth) and the Necronomicon, which enables powerful dark spells.
In the end, we only have to rename the underworld cities to associate them with the Chthulhi (Kalkar and Luthan are two obvious choices), and find an appropriate leaderhead for them (Chthulu?). As for the U-ga, we can add some Angels, to bring them in line with this
and with ERB's description of them.
I like this squaring of the circle; it is much less work.
Too bad about the Amazons (I loved that idea), but there are, as you've noted KA, quite a few in Pellucidar already. Perhaps they too will colonize the moon one day...