This shell is interesting because you can see the scar where the animal managed to survive a serious predation attempt, and then was able to repair the shell and carry on with its life.

It is also interesting because the shell had small knobs on the shoulder of the body whorl before the predation attempt, but became smooth on the shoulder after the predation attempt.

The paler shell has no knobs on the shoulder of the whorl, whereas the darker shell has knobs.

The knobless variety is less common, but it is far from rare.

I seem to find more of the knobless ones in certain locations, so maybe it is a genetic thing that is frequent within certain populations.