Megastomia simplex, common name the simple pyramid shell, is a species of sea snail, a marine gastropod mollusk in the family Pyramidellidae, the pyrams and their allies.
The white, rather solid shell has a smooth appearance. The length of the shell measures . The teleoconch contains 7ý rather flat whorls . They are a little angulated at the suture. The aperture is lirate within. Its plait is sharp and transverse.
The type specimen of this marine species was found off Port Jackson, New South Wales, Australia.