Among its many surviving stones and markers, one graveslab is notable for a different reason: it has vanished. The slab appears on a scholarly plan drawn up by R. A. S. Macalister during his survey of 1916 to 1917, marked close to the eastern wall of what he recorded as the Saint's graveyard, yet it was given no individual number in his catalogue. It left enough of an impression to be drawn, but not quite enough to be named.

Macalister's plan, published as plate XV of his survey, shows an undecorated slab, meaning it carried no inscribed cross, knotwork, or lettering of the kind found on more celebrated early Christian grave markers. Plain slabs of this type are common on early monastic sites across Ireland, often marking graves of monks or lay people associated with a community, their very simplicity a reflection of the period's austere commemorative traditions. At some point after Macalister recorded it, the stone disappeared from its documented position. Where it went, whether it was moved, buried, removed from the island, or simply subsumed into the ground, is not known. Its present location remains unaccounted for.