Queen Helmet Shell for sale in bulk for seashell décor, measuring between 5 inches and 5-3/4 inches. Queen helmets, Cassis madagascariensis,is a species of very large sea snail,  in the family Cassidae, the helmet shells and bonnet shells. Queen helmets occurs in the tropical Western Atlantic. The specific name "madagascarensis" literally means "of Madagascar".  Shells of Cassis madagascariensis are used in jewelry to make cameos. Queen helmets are large shells with a shiny oval face, with deep brown ridges around the mouth area in rich deep brown tones.