Erronea ovum, common name the egg cowry, is a species of sea snail, a cowry, a marine gastropod mollusk in the family Cypraeidae, the cowries.
The shells of these quite common cowries reach on average 22- of length, with a minimum size of and a maximum size of . The dorsum surface of Erronea ovum is smooth, shiny and generally dark brown, dark olive green or greyish, often with a darker wide trasversal band. They are egg-shaped (hence the Latin name ovum, meaning egg). The base and the margins are usually white or pale brown, with yellowish teeth, but in Erronea ovum chrysostoma the teeth are pink-orange. In the living cowries mantle is greyish, with long tree-shaped sensorial papillae.
This species occurs from Southeast Asia to the Southwest Pacific, along the coasts of Japan, East China, Thailand, Indonesia, Malaysia, Papua-New Guinea, western Australia, Philippines, Palau Islands, Solomon Islands, Micronesia and New Caledonia.
Erronea ovum lives in the tropical and subtropical zone, in shallow intertidal water up to 3- of depth, mainly on coral reefs.