A friend went up on Penmaenmawr on Friday and saw the ring cairn that you claim to be Circle 278:

http://www.themodernantiquarian.com/post/25505

and I agree with you: your photo is of Circle 278 and the others are of another feature (though I know not what).

In Prehistoric Wales (Lynch/Aldhouse-Green/Davies) there is a sketch plan of Circle 278 which shows it as a ring cairn with a wide bank within two circles of stones.

baz