Eulithidium cyclostoma is a species of small sea snail with calcareous opercula, a marine gastropod mollusk in the family Phasianellidae, the pheasant snails.

[1][2] The height of the dark brownish shell reaches 2 mm.

The broad, very obtuse shell consists of three whorls.

The shell is densely pointed or stained.

[3] The type locality is listed as "Cape St. Lucas, (Xantus)" (Cabo San Lucas, Baja California Sur, Mexico).