CIMRM Supplement - Zodiac. Santa Prisca, Rome, Italy
To the left of the main chamber of the Mithraeum are three side chapels. One of these, labelled Y, contains a monument which was a zodiac.
From Vermaseren, Mithriaca II: The Mithraeum at Ponza, p.16:
In the Excavations Vermaseren states (p.140) that the room had dark red stucco of the same colour as the fronts of the podiums; and the room had a layout, rather like a Mithraeum itself with two benches either side:
He goes on to speculate that it may have been the Mithraic equivalent of a baptistry.