"Felices sancte apostole" in F-Pn Latin 12044, an early 12th century antiphoner from St Maur-des-Fossés. The notes on Felices are C-DE-E, where the fragment has D-CD-D.
also "Felices sancte", from F-Pn NAL 1535, an early 13th century antiphoner from Sens. The melody starts C-DE-E and is, but for a few notes, the same as that from St Maur des Fossés.
4. so far I've only found two other manuscripts with this "Felices sancte" antiphon, but their melodies are different from this one! very similar in shape though, as if it got transmuted through transposition in different traditions.
what a fun #fragmentfriday chant page!