This broken piece of ammonite shows the delicate patterns on the shell, known as suture lines. These lines are formed from the folded walls that divide the shell into a series of hollow chambers. On the left side of the specimen, you can see how the smooth wall becomes folded towards the outside edge of the shell. That is where the suture line appears. The next line beyond it marks the chamber wall, creating the next chamber. In other words, the area between the two lines is the hollow chamber, now filled with crystal and the two parallel lines are the chamber walls. The folded face of the chamber wall is also known as a ‘cat’s paw’ in folklore, as some really do look like a paw.
Find out more about ammonites on the molluscs pages.