In all the history of the Federation, not every race made it into the august assemblies. Sometimes a planet would enter, last a few years, and then fall out when the world government collapsed, or were too far away to defend, etc.
These are the Foederati, natives of the planet Foederus. They managed to last long enough to get some surplus Seax-class destroyers, before things broke apart. Alas, not knowing the results of research, the Foederans mounted the nacelles in a dorsal configuration, not knowing that this limited the warp-field geometry in a way that degraded performance by 30%. Known as the Bernsheider effect, it meant that Federation mountings were side-by-side, but if you're the big dog in a small pond, you take what you can get.
Seax-class (saucer looks like an axe..what the hey), and alien Blenderbuss-class by me in Wings and Blender..enjoy..;)