Semilaoma costata, also known as the coarse-ribbed pinhead snail, is a tiny species of land snail that is endemic to Australia's Lord Howe Island in the Tasman Sea.

[2] The subdiscoidal shell of the mature snail is 0.7–0.8 mm in height, with a diameter of 1.3–1.5 mm, and a low to flat spire.

The sutures are impressed, with moderately closely-spaced radial ribs.

It has an ovately lunate aperture, and a moderately wide umbilicus.

[2] The snail is common and widespread in the North Bay and settlement areas of the island, living in plant litter.