Which capital and megacity's name translated means "the bellybutton of the waters of the moon"?

Mexico City

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After New Spain won independence from Spain, it was decided that the new country would be named after its capital, Mexico City, which was founded in 1524 on top of the ancient Aztec capital of México-Tenochtitlan. The origin of the name of the city comes from the Nahuatl language, where Mextli or M?xihtli, a secret name for the god of war and patron of the Aztecs, Huitzilopochtli, in which case M?xihco means "Place where M?xihtli lives".

The word M?xihco derives from the m?tztli ("moon"), xictli ("navel", "center" or "son"), and the suffix -co (place), in which case it means "Place at the center of the moon" or "Place at the center of the Lake Moon", in reference to Lake Texcoco. The system of interconnected lakes, of which Texcoco was at the center, had the form of a rabbit, the same image that the Aztecs saw in the moon. Tenochtitlan was located at the center (or navel) of the lake (or rabbit/moon).

With all due respect for the bellybutton, I'd be more inclined to lean towards this etymology:

The Nahuatl word Mexiko or Mexihko is composed of the root Mexi and the suffix -co that means "place" or "city." The full name of the city, Mexico-Tenochtitlan, means "the place of the Mexica in the cactus-stone," in reference to the image of the eagle perched on a cactus that grew from a stone, in the middle of Lake Texcoco. This image is represented in Mexico's coat of arms and flag.

http://www.sheppardsoftware.com/Mexicoweb/factfile/Unique-facts-Mexico6.htm