The Collaborative International Dictionary of English v.0.48:

Lemuria \Le*mu"ri*a\ (l[-e]*m[=u]"r[i^]*[.a]), n. [So named from
   the supposition that it was the original home of the lemurs.]
   A hypothetical land, or continent, supposed by some to have
   existed formerly in the Indian Ocean, of which Madagascar is
   a remnant. --Herschel.
   [1913 Webster]