We seem to have an abundance of these at a local reservoir and I find the shells all over the place when the lake is down. Must be a smorgasbord for the trash pandas. I have been wanting one of these big guys for awhile now and this is the first one I have found from the Olentangy River. This specific snail is about or a bit bigger than a Ping-Pong ball and it eats just about anything.

Updated: I have identified the species as Viviparis malleatus, or, Chinese mystery snail, Japanese trapdoor snail. They were brought here from Asia, specifically, East Asia from the tropics of Indochina to northern China and sold for food in Chinese food markets in San Francisco in the late 1800s. They were collected in the wild in Boston by 1914.