Recognition.
The best way to understand how a shell is made and to distinguish it from others is that of observing a sample and describe every little detail: shapes, colors, streaks, teeth, wrinkles, lips, turns, etc.. There are many books on the market for this purpose. But it's more important to compare the images with the shell on the books. It 's surprising to find out as between the photo and the sample is a perfect likeness. This allows us to be sure you have correctly classified a shell.