.. after this, a second circle of the same dimension, with only five large stones remaining; but with a circular cytt or house, 5 feet in diameter, inside the circumference. Our guide informed us that according to local tradition these were called cerrig y pryved, “the stones of the flies.”
Pryfed does mean flies, or bugs, or generally small creepy crawly things, according to my dictionary. ‘Pryfaid’ doesn’t feature at all? or is it a kind of made up plural?
From some Correspondence from H. Longueville Jones to Archaeologia Cambrensis in vol 1, p76 (1846).