In the process of doing some Muvian reasearch (possibly for a future project), I stumbled upon this:
http://www.newdawnma...unken-continent
Haughton is a qualified archaeologist who specializes in writing about "mysterious" history. As opposed to the wild-eyed quackery we usually see, his books are pretty level-headed and accurate.
For Howardian purposes, the whole Lemuria/Australia thing can be thrown right out the window. REH's concept of Lemuria was radically different than that proposed by Haeckle. However, what I really like about the article linked above is the very thorough treatment given to the entire history of the Lemuria/Mu concept. I've never seen the entire topic (with relevant up-to-date news) handled better.
I hope Haughton's article will serve as a handy primer for anyone wanting to get a grip on what's been said about Lemuria/Mu over the last 100+yrs. 
One thing in the article that I want to "correct" somewhat is this:
It was James Churchward who first posited the theory that the site of Nan Modal, on Pohnpei Island in the North Pacific Ocean, was one of the seven cities of ancient Mu / Lemuria.
That's basically true. However, A. Merritt, in his novel, The Moon Pool (1919), posited Nan Madol as the point of entry to the underground world of "Muria". Thus, IMO, Merritt served as the (or "a") link between Blavatsky's "Lemuria" and Churchward's The Lost Continent of Mu, which came out 7yrs after Merritt's novel.
Not a bad historiogrphy of Lemuria/Mu though he makes a couple of minor mistakes.
Here's what I came up with for a bibliography for Lemuria and Mu pre-1927, annotated and in chronological order. These are the major works, though there are a lot of minor theosophical and occult publications that mention Lemuria.
Non-Fiction
Sclater, P. "The Mammals of Madagascar"
Quarterly Journal of Science (1864) [Indian ocean Lemuria first named]
Brasseur de Bourbourg, C. E.
Manuscrit Troano (1869-70) [erroneous translation of Troano Codex where "Mu" first appears]
Wallace, A. R.
The Geographical Distibution of Animals (1876) [discusses Sclater's Indian Ocean Lemuria]
Sinnett, A. P.
Esoteric Buddhism (1883) [First appearance of Theosophical Atlantis and Lemuria]
Haeckel, E.
The History of Creation (1884) [Indian Ocean Lemuria as homeland of mankind]
Jacolliot, L.
Occult Science in India (1884) [Pacific Lemuria; one of Blavatsky's dubious sources]
Blavatsky, H.
The Secret Doctrine (1888)[Theosophical Lemurians as Third Root Race]
Le Plongeon, A.
Queen Moo and the Egyptian Sphinx (1896) [based on de Bournbourg equates Mu with Atlantis]
Scott-Elliot, w.
The Story of Atlantis (1896) [Theosophical; Lemuria in Pacific and Indian Oceans]
Phelon, W.
Our Story of Atlantis (1903) [Theosophical; briefly discusses Lemuria]
Scott-Elliot, W.
Lost Lemuria (1904) [Theosophical; more detail on Lemuria; both S-E books based on past life memories of Leadbeater]
Anderson, J.
Riddles of Prehistoric Times (1911) [Chapter on Lemuria; following Haeckel]
Steiner, R.
The submerged Continents of Atlantis and Lemuria (1911) [Theosophical; based on Leadbeater again]
Besant, A. and C.
Leadbeater Man: Whence, How, and Whither (1913) [Theosophical; Leadbeater in his own words]
Steiner, R.
Atlantis and Lemuria (1923) [Revised edition of earlier book]
Brown, J. M.
Riddle of the Pacific (1924) [Easter Island as remnent of Pacific continent]
Spence, L.
Atlantis in America (1925) [chapter on Lemuria based on Brown's book]
Scott-Elliot, W.
The Story of Atlantis and the Lost Lemuria (1925) [combined edition]
Churchward, J.
Lost Continent of Mu (1926) [Mu as Pacific continent]
Fiction
Scott, G. F.
The Last Lemurian (1898)
Oliver, F.
A Dweller on Two Planets (1905) [First time Lemuria is connected with Mt. Shasta]
Merritt, A. "The Moon Pool"
All-Story Weekly (1918)
Merritt, A. "Conquest of the Moon Pool"
All-Story Weekly (1919)