Triton, the god of the sea, is customarily shown blowing a trumpet fashioned from this foot long shell.  Throughout the ages man has used this shell as a horn, but certain tribes made the "blowing hole" on the side of the shell, whilst others cut off the apex at the narrow end.  The operculum of the triton is a large, heavy, horny trapdoor.

Triton shells feed mainly on star fish as seen in my photograph and when hungry will even eat the famous "Crown- of -  Thorns " starfish.