The Adelphousians were a type of sapient alien lifeform, a civilization native to class M homeworld planet Adelphous IV, located in the Adelphous star system in the galaxy's Beta Quadrant. (TNG novel: Takedown)
History and specifics[]
In the 24th century, the Adelphousians' homeworld was near the boundaries of Federation space, and was a destination of the Starfleet starship Enterprise-D in the 2360s decade. (TNG novel: Takedown, TNG episode: "Data's Day")