These ammonites, Aulacostephanus, can be beautifully preserved with almost pearlescent calcite crystal. This is not a complete specimen; note how there is a suture line (wavy line) showing near the end of the shell. This is probably the last of the chambered shells, but most of the body chamber is missing, either not preserved or lost when it was collected. This genus of ammonite is important for dating the Kimmeridge Clay.
Find out more about ammonites on the molluscs pages.