Marsh Periwinkle and they don't do well in reef tanks, they prefer to be out of the water a majority of the time and eat algae growing on marsh grasses, pilings, trees, etc. above the water line.
You can however find Caribbean nerites in some parts of Florida, if you drive down to the East coast of South Florida you can find them by the dozens on beaches with rock outcroppings and such. My girlfriend and I collected around 20 for her mother's reef aquarium at Coral Cove Park in Juno Beach/Jupiter and I believe most are still living after almost a year.