The Southern Flatcoil Snail
Polygyra cereolus (Mühlfeld, 1816), reaches at most 18 mm (about 0.7 inch). The species is found in Florida and other parts of the southeastern US. As the name implies, flatcoil snails have "flat" shells with a relatively large number of tightly coiled whorls.
The shell opening bears a characteristic tooth-like projection (see below). The great photo above of a living snail was recently taken by Lorin Buckner in Fort Myers, Florida.