MLA

Hilles, Frederick W. (Frederick Whiley), 1900-1975. Marlowe, Christopher. Box 35, folder 920. undated. https://collections.library.yale.edu/catalog/2007756.

APA, 6th edition

Hilles, Frederick W. (Frederick Whiley), 1900-1975. (["Box 35, folder 920"])(undated)[Marlowe, Christopher]. https://collections.library.yale.edu/catalog/2007756.