'Jesu joy of man's desire' by Johan Sebastian Bach. The Byrds also took the melody for a guitar solo on an early song - a b-side, I think, but can't remember which one. As for Lady Lynda, two thoughts... 1/ Al Jardine wrote it for his wife of 25 years... and they split up not long after.... and 2/ The Light Album (from which it comes) isn't much good is it?! Though there are some amazing early versions of the Dennis Wilson song Baby Blue available on the Net... anyway, enough rambling. Hope this helps!