Hard clams (Mercenaria mercenaria), commonly called quahaugs; public domain USDA photo on Wikipedia.
Official State Shell of Rhode Island
Rhode Island designated the quahaug as the official state shell in 1987. A shellfish native to the eastern shores of North America, quahaugs (or hard clams) are one of many unrelated bivalves people refer to simply as "clams." Several states have adopted seashell symbols. All Aquatic-Life Symbols
The name "quahog" comes from a Native American (Narragansett) word "poquauhock." The quahog's scientific name, Mercenaria mercenaria, is from the Latin word for "wages" (Native Americans used quahog shells to make beads that they used as money, or "wampum").