Please Identify This

[Buddym]

Here is a shell which came into my hands recently which I would like to identify. It is 6 inches (153mm) long and 5 inches (127mm) wide.

[paul monfils]

This is a juvenile specimen of one of the world's largest shells - Cassis cornuta, the Horned Helmet.  The females have the small knobs around the edge of the spire, like yours.  The males have very large, thick projections, from which the species gets its name ("cornuta" meaning "horned").  Large specimens can reach about 16 inches in length, occasionally 18 inches. Here you can see a very large male, followed by a smaller adult male, then a small female like yours, followed by another male: http://www.gastropods.com/4/Shell_804.shtml