This is the School of Athens fiasco all over again. The mosaic:
Appears to portray six Greek philosophers in various attitudes of respose, gathered around a central figure leaning against a tree, and thought to be Plato. As is frequently the case, no one can know for sure who the artist intended to portray. I have seen the second man from the right identified as Epicurus, though this is not the common assessment.
In favor the Epicurus argument is this statue:
In both statue and mosaic, the subject is featured with the right foot forward and the right forearm bent upward, holding a scroll. In the actual statue the head and right arm were lost, and the work was fitted with a different head and different limb. The hypothesized scroll in the hand was of course lost with the limb.