Making sense of Griffith's Valuation entries

I found an entry in Griffith's Valuation that may be a great-great-grandfather; the only other info I have on him so far comes from his children's birth & baptism details:

http://imgur.com/a/veJlK (top image)

I have a few questions:

1) How do I work out the location on the map from the entry? There seems to be four columns of co-ordinates in the "Reference to Map" column:

1) a number
2) a upper case letter
3) another column of upper-case letters (and in Stephen's case, what appears to be either an X or a delta symbol?), and
4) a lower-case letter.

So then went to the map by clicking on the relevant icon:

http://griffiths.askaboutireland.ie/gv4/single_layer/i8.php?lat=&longt=&dum=0&sheet=10&mysession=2506447103644&info=&place=&county=WEXFORD&placename=MONEYDURTLOW&parish=KILRUSH&country=Ireland&union=&barony=SCARAWALSH

I'm presented with a big red rectangle inside a white circle; any idea of the meaning of these? EDIT: Found this out from the, er, "Guide to Maps" button.

But I've no idea how to translate the four-column-coordinate above to this map, which at most seems to show only two coordinates for any area (number and letter).

PLus, another question: Stephen's co-tenant was a Mary Kehoe - might this have been his wife? Unusually to use a maiden name in this context, or even have a wife as a joint owner at this period, I would have thought.

Any help appreciated,

P.