Tonite's graph shows the growth of foot relative to that of shell in the land snail Euxina circumdata. The blue line is a hypothetical case where growth is isometric, that is, the lengths of the foot and the shell remain equal to each other during growth. The red circles are the actual data for Euxina circumdata.
The largest snail was an adult, while the rest were juveniles. It is clear that in very small snails the foot is almost as long as the shell. But the shell grows much faster than the foot. As a result, in adult snails, the foot is shorter than half of the shell.
What this all means may the be the subject of a future post provided that I can come up with a meaningful explanation.