The Lord Howe flax snail or the Lord Howe placostylus, scientific name Placostylus bivaricosus, is a species of large air-breathing land snail, a terrestrial pulmonate gastropod mollusc in the family Bothriembryontidae. This large snail is found only on Lord Howe Island off the east coast of Australia. Its conservation status has declined from common to endangered since rats were accidentally introduced to this World Heritage island in 1918.