As you walk around the top of the ridge from tomb 52 towards tomb 51 (Listoghil - the central cairn) look down and you will see two monuments, 48 & 49. This one is like 55, a low boulder burial type structure, but it may well have been a totally trashed dolmen type.
The capstone lies on nothing more than a pile of stones, but it is beautifully shaped. It is an odd wedge shape with several deep cups in its upper surface. Then underside is very flat.
This is an explanation of (and a bit of a disclaimer for) the coordinates I provide.
Where a GPS figure is given this is the master for all other coordinates. According to my Garmin these are quite accurate.
Where there is no GPS figure the 6 figure grid reference is master for the others. This may not be very accurate as it could have come from the OS maps and could have been read by eye. Consequently, all other cordinates are going to have inaccuracies.
The calculation of Longitude and Latitude uses an algorithm that is not 100% accurate. The long/lat figures are used as a basis for calculating the UTM & ITM coordinates. Consequently, UTM & ITM coordinates are slightly out.
UTM is a global coordinate system - Universal Transverse Mercator - that is at the core of the GPS system.
ITM is the new coordinate system - Irish Transverse Mercator - that is more accurate and more GPS friendly than the Irish Grid Reference system. This will be used on the next generation of Irish OS maps.