MLA

Sacro Bosco, Joannes de, fl. 1230. De sphaera. [ca. 1400?]. https://collections.library.yale.edu/catalog/9998997.

APA, 6th edition

Sacro Bosco, Joannes de, fl. 1230. ([ca. 1400?])[De sphaera]. https://collections.library.yale.edu/catalog/9998997.