Dytallix B is a mining planet where Walker Keel held a secret meeting to warn Picard of a conspiracy in Starfleet.
Dytallix B is one of several mining planets in the Mira system, used by a mining company and left largely abandoned. In Conspiracy Captain Walker Keel asked Picard to meet him there in person, in the deserted mine workings, away from any chance of being overheard.
At the meeting Keel and two other captains, Tryla Scott and Rixx, told Picard about strange orders and suspicious deaths in Starfleet. The meeting set Picard on the path to Earth, where he uncovered the alien parasites controlling Starfleet officers.