Near Ballina in County Mayo, a site logged as a possible mound has proved stubbornly elusive. Ordnance Survey maps from both 1837 and 1930 show nothing that resembles a mound at the recorded location, and the supporting files contain no independent references to one ever having been observed there.

The most plausible explanation is that the record is a duplicate, pointing without realising it to something already catalogued nearby. The likely candidate is a megalithic tomb, a prehistoric burial monument, which appears on the Ordnance Survey six-inch maps under two evocative names: 'Fert Echtra' and 'Princess Grave'. A fert, in early Irish, denotes a grave mound or burial place, and the name Echtra carries associations with otherworldly journeys in medieval Irish literature, lending the site a quietly mythological atmosphere. It is possible that the tomb was once covered by a cairn, a mound of piled stones rather than earthwork, and that this covering gave rise to the separate mound record in the first place, before anyone had properly checked whether the two entries described the same place.