Species 312
From Memory Alpha, the free Star Trek reference.
Species 312 is the Borg designation for a race which employed a tetryon-based technology.
The species visited the planet Ledos, several hundred years before 2377, and built a tetryon-based energy barrier to protect the primitive Ventu from the harmful actions of the other Ledosians.
The species was assimilated by the Borg sometime before 2374. (VOY: "Natural Law")
