Soldarin
The Soldarins are a long extinct species who are believed to have originated in the Omicron Persei System. That system is in the Beta Quadrant.
The species appeared to have become extinct roughly 3,000 years ago, although remnants of their civilization still remain.
The Soldarins were an advanced species, showing advanced medical, computer, energy production and holographic technology. The fact that the Soldarin Archives on Kadyl were still fully functional after nearly three millenia without maintenance is a testament to their abilities.
The Soldarin were first discovered by the United Federation of Planets in 2414 when the USS Rosenante discovered the Soldarin Archive Probe in deep space. Following the Probe led the ship to a Class H moon, where the Archive was located.
Physiology
Not much is known about the Soladrin physiology. They did not breathe oxygen, instead using Helium and Methane as their primary respiratory gas. They possessed excellent eyesight due to large oversized eyes and it is speculated that they were capable of seeing into light spectrums that were beyond the capability of a human. In addition to their eyesight, it is believed that they also possessed keen sense of hearing.
No remains of the Soldarins were found, so beyond basic visual images and supposition, there is little else known about them.
The Soldarins were first seen in the USS Rosenante Mission Lest We Forget