Diatome (1962–1985) was a British-bred Thoroughbred racehorse owned and bred by the French banker, Baron Guy de Rothschild.A descendant of Prince Palatine, Diatome won important races in France but had the bad luck of being foaled the same year as superstars Sea-Bird and Reliance. He finished second to Reliance in the Prix du Jockey Club and the Grand Prix de Paris. In the Prix de l'Arc de Triomphe, Diatome finished third behind Reliance and winner Sea Bird.