MLA

Bullitt, William C. (William Christian), 1891-1967. General. Box 180, folder 2 - 6. 1934-1936, undated. https://collections.library.yale.edu/catalog/10687853.

APA, 6th edition

Bullitt, William C. (William Christian), 1891-1967. (["Box 180, folder 2 - 6"])(1934-1936, undated)[General]. https://collections.library.yale.edu/catalog/10687853.