The IRW Terix was a Romulan D'deridex-class warbird in service during the 24th century. Commanded by Commander Sirol, the Terix discovered a hull fragment from the Starfleet testbed vessel USS Pegasus in the Devolin system in 2370. The warbird was subsequently ordered to find the rest of the ship. When the USS Enterprise-D arrived with the same mission, Sirol claimed that the Terix was investigating gaseous anomalies.
After the Enterprise-D entered asteroid gamma 601 to salvage the Pegasus, the Terix sealed the starship inside during some "inadvertent geological experiments." The Terix offered to transport the crew of the Enterprise-D out, but the starship escaped on its own using the Pegasus's interphase cloaking device. (TNG: "The Pegasus")
The Terix was Tomalak's flagship in a face-off in the Romulan Neutral Zone in an alternate timeline created by Q. (TNG: "All Good Things...") Template:D'deridexClassStarships