The Knobbed Whelk is Georgia's State Shell. Often called the "Georgia Conch", for it's similarities, but it is not a Conch. Conch's are gathered and eaten by the natives of the Caribbean and Florida as Conch salads, Conch burgers, Conch stew, Conch fritters, etc. The animals have a very muscular foot, which has to be pounded pretty hard to soften the fibers before cooking. Some people in Georgia like to do the same with knobbed Whelks, hence the name, "Georgia Conch".
In the photo, the Whelk inside the jar has extended it's foot and mouth, while the Whelk on the outside has retracted it's foot and mouth. Also, notice the operculum - a piece of shell attached to their foot that forms a lid when the foot is retracted.
Whelks have a special "grinding tool" in their mouth, called a radula. This allows them to grind through the thick shells of other mollusks and eat the animal inside.