This snail, a native of eastern U.S., is known as Lobosculum pustuloides, although it may not actually belong to that genus (family Polygyridae). For today, however, I will ignore its uncertain taxonomic placement and instead discuss the hairs that cover its shell.
The hairs grow out of the periostracum, the thin skin-like layer that covers the outside of the shell. There are several species of land snails that have similar hairy shells. For example, in the U.S. the species in the genus Stenotrema, also in Polygyridae, too have hairy shells.
What are the hairs for?
To answer that question, Pfenninger et al. (2005) studied the members of the European land snail genus Trochulus. Their analyses show that the habitats of the Trochulus species with hairy shells tend to be wetter than those of the species with hairless shells. They also did some tests that showed that on a wet leaf surface a larger minimum force was necessary to move hairy shells than hairless shells. So they speculate that the hairs help the snails stick to wet surfaces such as the leaves of plants that they apparently climb when they are feeding. It is not clear to me, however, why the snails' already sticky feet and slime wouldn't be strong enough to secure them to the plants they are on.
Would their findings apply to L. pustuloides and the other hairy U.S. snails? These snails seem to spend most of their time in the litter or on rotting trunks on the ground. I don't think they are in any danger of falling down from places high above the ground.
One possibility not considered by Pfenninger et al. is that the hairs may have an antipredatory function. They may, for example, deter the carnivorous snail Haplotrema concavum that drills thru the shells of its victims if it can't fit its head thru their apertures.
Lobosculum pustuloides is a small snail. The shell of this particular adult was 4.2 mm across.
Markus Pfenninger, Magda Hrabáková, Dirk Steinke, Aline Dèpraz. 2005. Why do snails have hairs? A Bayesian inference of character evolution. BMC Evolutionary Biology 5:59 (4 November 2005). pdf