Counting shell whorls

It is important to count the number of whorls in a shell in order to establish whether it is an adult. Juveniles are very difficult until experience with adult shells has been gained.

How to count whorls 

In the case of shells which are wider than they are tall, look at the apex and imagine a line across the diameter of the shell. Start the count at the line across the semicircle at the apex, as in the diagram. Passing round the whorl, the count is increased by one each time the extension of the line is passed, and any "remainder" is estimated as a fraction – in the diagram to the left, there are 3½ whorls.

Counting whorls

When counting the whorls on a shell that is taller than it is wide, it is probably easier to count from the body whorl up towards the apex, with the mouth opening facing the observer – in the diagram to the right, there are 6 whorls.