Syntagus Theluv, also known as T-B 13, was a planet, the thirteenth planet of the Tri-Betaline star system. With a class M environment, this world was the homeworld of a humanoid species known as the Theluvians.
In 2364, the USS Enterprise-D entered orbit of the planet to conduct a general survey. As the sensor scans were being conducted, the Enterprise was contacted by the Theluvians, who expressed their desire to meet the Enterprise crew and establish a dialog with them. With this in mind, Commander William T. Riker led an away team down to the surface, but instead of finding themselves in the planet's capital city, they found themselves in a forest clearing, and under attack by a Tripolian hellblazer.
Eventually, the away team were able to overcome the hellblazer and learned that even though it appeared that adults were attacking them, it turned out that the Theluvians age in reverse, and the children are the adults on Syntagus Theluv. (TNG comic: "... Where No One Has Gone Before!")