The fragment consists of a single page, preserved in a modern folder (assigned the shelfmark Librone 3bis in November 2020) together with Fragment 2. Only the upper part of the original folio is extant. Similarly to Fragment 2, it was apparently restored during the 1950s and then forgotten in the Archive of the Veneranda Fabbrica until March 2019. No data have been retrieved about its original position and the circumstances leading to its present state. It seems to be the first folio of an otherwise lost gathering. The recto contains empty staves, with fragmentary original foliation in the top right corner. The verso contains the Cantus and Tenor (incipit only) of an anonymous Magnificat (with concordance in Librone 1). Based on the size, mise en page (with presumably 10 staves) and scribal hand, it might have formerly belonged to Librone 3.