With a record from 1974, this is one I've wanted to catch up with, and it turned out to be one I've eyed with suspicion for a while but not ID'd. Pulled from the rocks in the burn, this dingy moss closes the gap on species recorded but not seen by me at Cullaloe.
Leaves c2mm, margins entire, cells c. 3 times as long as wide, nerved to beyond half way but not to tip
Leptodictyum riparium, Kneiff's Feather-moss
BBS Field Guide page