I skipt #21 for a few reasons: I wasn't familiar with the tune (which has been the case for the last few tunes, so I wanted one I did know), and I couldn't get a good sense of what it was supposed to sound like because it consists of long note values and rests. So I did "St. Flavian" instead because it's the next hymn tune and because I am familiar with it.
It's probably just coincidental, but it occurred to me that "St. Flavian" starts with the same four notes as "Tallis' Canon."