S Antonin Historialis: Pars III. Two leaves of a Credo, previously pastedowns. One version for 3vv is in F-APT 16 and 5 other sources, attributed to Sortes/Sortis. The fourth voice appears to be unknown. Also fragment of a Gloria (beginning at Laudamus te). The front & rear boards have mirror image offsets of the now-lifted pastedowns.
See also Lerch's reconstruction of these and other fragments as 'F-CA(n)'.