Hermeticus II was a planetoid in the far reaches of the Neutral Zone. It was placed under quarantine by the United Federation of Planets in the mid-24th century after the USS Independence was lost investigating it.
In 2368, the USS Enterprise-D and the Romulan D'Kazanak-class Warbird IRW Syrinx rediscovered the planet. Further investigation revealed that Hermeticus II was in truth a starship, which was spherical in shape. It was inhabited by the Ambimorphs. (TNG novel: The Romulan Prize)