A Federation colony whose supposed environmental failure was reported in a distress call during the Romulan plot of 2368, a diversion meant to draw the Enterprise-D away.
Dulisian IV is a Federation colony mentioned in the Next Generation episode Unification II.
While the Enterprise-D waits near the Neutral Zone, watching three stolen Vulcan ships on their way to Vulcan, a call for help arrives from the colony reporting a massive failure of its environmental systems. Riker suspects that the timing is too convenient.
He is right. The call is part of Commander Sela's scheme to keep Starfleet occupied while a Romulan invasion force, disguised as a peace delegation, lands on Vulcan. A warning from Spock, Data and Picard on Romulus exposes the plan, and the Romulans destroy their own troop ships.