This last one bothers me a bit. It is certainly a fine thing to name features of another world after your favourite megalithic monuments, but most of those that have been commemorated in this way long pre-date the Celts! The list of places on Europa named in this way is as follows:
Butterdon Linea - after the stone circle and stone row on Butterdon Hill in Dartmoor
Callanish (large ringed feature) - after stone circle in the Hebrides
Corick Linea - after stone circle and stone row near Draperstown
Drizzlecomb Linea - after another Dartmoor stone circle and row
Drumskinny Linea - after stone circle near Fermanagh
Kennet Linea - I suspect after the West Kennet Avenue near Avebury
Mehen Linea - slightly baffles me; supposedly a "stone row in Brittany" but I don't find any monument with that name; could be an error for "Menec"?
Merrivale Linea - after another set of stone circles and rows on Dartmoor
Sharpitor Linea - yet another Dartmoor alignment
Staldon Linea - Once again, Dartmoor, though usually spelt Stalldown
Tormsdale Linea - the explanation says this is after an Irish stone row, but in fact it is in Caithness
Yelland Linea - after a now buried stone alignment in North Devon (but, for once, not on Dartmoor)
I think the IAU might need to do a little more vigorous fact-checking. Apart from anything else, the geographical balance is a bit surprising - only one name taken from Brittany, and that apparently wrong!