Emperor Helmet Snail

The maximum recorded shell length is 409 mm. The organism has no vertebra. It has a large, heavy shell, with a short spire. This shell typically has three rows of blunt knobs and smaller lines of spiral folds. It has an elongated aperture with folds on both sides of the inner aperture. This shell color varies from white to tan and may have brown markings and blotches. The species of Cassis Madagascariensis (Queen Helmet Mollusk) can be distinguished by their size and the number of spines on their shell. C. Madagascariensis Lamark can be identified more easily. This is because it has fewer and larger spines than most other species. The topmost spine is notably larger than the rest of the spines.

This species inhabits the tropical Western Atlantic, the Gulf of Mexico and the Caribbean Sea. The name "madagascarensis" means "of Madagascar", but this was a misunderstanding of the type locality by the original author.

Shells are used in jewellery to make cameos. In the Maldives the shell is boiled and the boiled water is used as a traditional remedy for flu and fever.