The T'lli Betans were the native species of planet T'lli Beta. In 2367, the USS Enterprise-D was en route to the T'lli Beta system to meet the T'lli Betans before it was ensnared by the gravitational pull of a cosmic string fragment which a group of two-dimensional lifeforms were attempting to enter. (TNG: "The Loss" ) This species was only mentioned in dialogue.