A characteristic of the Murex shell is that it has spikes or spines shooting out all over it. Finding one is good shape is difficult because of the rolling in the surf and sand which breaks off the spikes.
Mine is was purchased many years ago and has broken spikes, but is still pretty. BUT, not all shells in the Murex family have these spikes. Some have a frilly look, such as the “Festive Murex” and “Frill-Wing Murex” from the US west coast.
The Giant Eastern Murex averages 5 to 7 inches high and the West Indian Murex is 3 to 6 inches high.
According to Pensacolas Greatest Seashells blog, finding a Murex is not always easy, and finding one in great condition is ever tougher. They show three types on their blog, the Apple Murex, Rose Murex, and Giant Eastern Murex.
The one I own, pictured here, is the Pink Murex and I don’t see it listed in my reference book, but the book only covers the east and west coast of the USA. The link I have provided says theirs was found in Mexico -Peru and I have difficulty finding any other information.
This one is 5 1/2 inches long and 3 1/2 inches high.