Compare the shell that you have to the photos of the shells in our web collection. It will be helpful to decide if you have found a univalve or a bivalve. Univalves are the shells of gastropods. They are one piece and usually have a spiral. They are assymetrical.
Examples are conches and whelks.
Bivalves have two distinct shells joined by a ligament. Clams and oysters are examples of bivalves. Some are symmetrical. Keep shells away from direct sunlight and extreme heat. Pill vials and small plastic boxes are a excellent containers to store seashells.