"...as XP for
ekatontapxos (OGI 678 note 9; JRS xviii 1928 p. 171 no. 38)"
The source called "OGI" = Dittenberger, Orientis Graeci Inscriptiones selectae, II, 1905,
https://archive.org/stream/orientisgraeciin02dittuoft#page/422/mode/2up
No. 678, from Djebel-Fateereh in Egypt, p. 423, n. 9, commentary:
"It is interpreted by Letronne and Franz as
x(ilia)p(xw). To me, however, there seems to be no doubt that it rather means
ekantontapxos (centurio). First, the form of the sign itself shows that P (that is,
ekaton), not X, is the primary part of it; moreover, it appears to have been usual for a centurion to be put in command of the mine from the Latin inscription of the same place, which is produced by Franzius,
Annius . Rufus ) (i.e. centurio) leg(ionis) XV Apollinaris . praepositus ab . Optimo . Traiano . operi . marmorum . monti . Claudiano . v(otum) . s(olvit) . l(ubenti) . a(nimo). Finally, the same abbreviation also appears elsewhere, where there is no room for doubt that it signifies
ekatontapxos or
ekatontapxia. Compare n. 208^2.”