This site is known locally as the Dolmen of the Four Maols.
The tomb is not actually a dolmen but a Kist.
The site is located on the outskirts of Ballina town above the railway station. It looks like at some stage one of the side-stones has been removed from the tomb (first image) and left lying a few feet away.
This tomb is well worth a visit but prepare yourself for the OPW sign at the front of the tomb and various masts, fences and phone lines (all shown in their full glory here).