File:Conor Roe O'Brien Tomb Effigy Drawing.jpg

English: Representation of tomb effigy of Conor O'Brien in Corcomroe Abbey.
Based on a study of many images of the effigy which were collected going back as early as 1949 combined with a study of written accounts of the monument describing details which were either obliterated since their describing or were not evident from these photographs.
The shape of the crown was derived from the remnants of it still visible on the monument, with one eroded point still visible on the right hand side. It is further speculated in a text about it's twin monument (that of King Felim O'Connor, died 1265) which possesses the same clothing and attitude that: "Judging from the fragment which remains, this crown was formed by a fillet some two or three inches deep, from which sprung three obtuse points - one at each side of the head, and one in front - a form sometimes seen on regal monuments of the thirteenth century."^[1]
This is likely the same form of the crown on this monument as their features are generally identical.
Westropp describes the monument thus:
"Let us add to these brief notes that the costume of the effigy of King Conor na Siudaine O’Brien in Corcomroo Abbey consists of a pleated ungirt tunic, falling half-way down the thigh; long cloak; close hose; pointed shoes, held round the ankles by buckled straps, and open on the instep. The crown, though nearly broken away, preserves on its inner side a trefoil; and the sceptre ends in the same; a reliquary or pendant is hung with long bands round tho neck ; the face is dean-shaved, and the hair worn in heavy locks falling to the shoulders; the head is supported by a plain pillow; while the feet rest on a richly embroidered cushion."^[2]
This "trefoil" or fleur de lys described is a quite ornate carving which I think I have seen in certain photos (appearing to rest at least partially on the parting hair), but was nonetheless too small to give a meaningful representation of in this image. Nevertheless the artisan who completed these two monuments had a fondness for this symbol and reportedly included it in the end of the white rods held in both sculptures.
See this category (https://commons.wikimedia.org/wiki/Category:Conor_O%27Brien) for several public domain images of the original monument.