MLA

Processionale (Pars Aestivalis) for the Collegiate Church of St. Genesius at Clermont-Ferrand. 0AD. https://collections.library.yale.edu/catalog/9998920.

APA, 6th edition

Processionale (pars aestivalis) for the Collegiate Church of St. Genesius at Clermont-Ferrand. (0 C.E.). [Manuscripts, Medieval France 15th century, Medieval and Renaissance Manuscripts in Beinecke Library]. https://collections.library.yale.edu/catalog/9998920.