WASHINGTON (AP) — A large conch shell overlooked in a museum is now thought to be the oldest known seashell instrument, and it can still play a tune. French researchers estimate it to be around 18,000 years old. It was found in a French cave in the 1930s and was assumed to be a ceremonial drinking cup. Researchers recently took a fresh look and determined the shell had been modified to serve as a wind instrument. They invited a musician to play it and the horn produced a deep, plaintive bleat, like a foghorn from the distant past. Their research was published Wednesday.