The Leyron were a species native to the planet Malkus IX.
They were considered unique as they were one of few known species to have developed a written language significantly before developing a spoken or sign language. (TNG: "Loud As A Whisper")
Kathryn Janeway once studied the gestural idioms of the Leyron, which she found more comprehensible than the non-verbal language of the Tak Tak. (VOY: "Macrocosm")
This species was only mentioned in dialogue.