Not what it appears to be
This is an ammonite, not a snail! Ammonites from the Lower Chalk are very distinctive and evolved into a range of bizarre forms. In this case, rather than developing as a flat spiral like nearly all other ammonites, it coiled into a spire, like a snail. It is thought that these ammonites may have been filter feeders, or that they bumbled along just above the sea bed picking up food.
Find out more about ammonites on the molluscs pages.