These shells can be seen through, (though the lighting was bad in the attached photographs) two species are listed in my shell identification book, with a second verification in another Shells book. Baby Ear is the name of this particular shell.
The two species, are Maculated Baby's Ear Sinum maculatum, measuring 1-2", found throughout the Carolinas and West Coast of Florida.
Common Baby's Ear, Sinum perspectivum, 1-2", and found throughout Virginia through Florida, Gulf of Mexico and West Indies.
White Baby-Ear Sinum perspectivum (Say)
Description: (1 3/4 inches) Flat, smooth, ovate shell. Well-named. Low spiral cords on upper side of whorl. When alive, almost completely covered by mantle; resembles a piece of white gristle. No umbilicus. Large, round aperture. No operculum.
Color: White exterior. Pale brown periostracum. Yellowish cream mantle.
Habitat: Commonly found in shallow offshore waters and washed onto ocean beaches.
Range: Maryland to Brazil.
Notes: Also called Common Atlantic Baby-Ear.
Source: Seashells of North Carolina, North Carolina Sea Grant College Program