MLA

Petrus, Comestor, active 12th century. Historia scholastica, etc. [between 1250 and 1300]. https://collections.library.yale.edu/catalog/9998858.

APA, 6th edition

Petrus, Comestor, active 12th century. ([between 1250 and 1300])[Historia scholastica, etc]. https://collections.library.yale.edu/catalog/9998858.