Species 312 was the Borg designation for a race which employed a tetryon-based technology.

Based on their their technology, it was speculated that the species may have been the one that visited the planet Ledos, several hundred years before 2378, and built a tetryon-based energy barrier to protect the primitive Ventu from the harmful actions of the other Ledosians.

Members of the species were assimilated by the Borg sometime before 2374. (VOY: "Natural Law")

This species was only mentioned in dialogue.
The Star Trek Encyclopedia (4th ed., vol. 2, p. 179) speculates that this species could have been the Preservers.
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