Land which rises or disappears under the sea during severe pole shifts almost invariably inspires legends, and if the land is inhabited or frequented during hunting expeditions, living patterns of the survivors are dramatically disrupted.
Atlantis was land near the current continent of Europe, which was pulled into the Atlantic during the continental rip that accompanies violent pole shifts and thus disappeared dramatically under the sea. This demise was assisted by extraterrestrials, who took advantage of the natural cataclysm to adjust the balance in spiritual orientation influencing developing human spirits, in line with a determination by the Council of Worlds that such an adjustment was needed. Atlantis had been essentially invaded by the giant hominoids from the 12th Planet, who prior to the quarantine that is now in effect were considered simply another hominoid race within your Solar System. Interactions between humans and these hominoids were allowed to proceed without interference, but increasing slavery of humans by these giant hominoids was tripping the balance so that humans were less and less free to choose their orientation based on their true feelings and increasingly influenced by feelings of helplessness. Thus, an adjustment was required.
Lemuria was land on the other side of the world, in the Pacific, which without interference slipped under the waves during a similar pole shift. As with most pacific lands, Lemuria was inhabited by the easy-going peoples of the South Pacific. Thus where the legends about Atlantis are centered around the relative strength and power that Atlanteans had, the legends about Lemuria center around their peaceful outlook. Atlanteans, being the giant hominoids which like humans today had technology, including the use of crystals for communications, seemed god like, and thus the destruction of that land is surmised to be by their own hand. Lemurians, great in number as the land was more than the scattering of islands that exist in the Pacific today, have been deified as a special spiritual race, and all manner of benefits to occur should they somehow return. As is often the case, these lands, in death, are more than they were in life.