MLA

Scheuer, Steven H., 1926-2014. The Turning Point #11 Halsted Welles. Box 1, folder 4. n.y. Jun 21. https://collections.library.yale.edu/catalog/17101430.

APA, 6th edition

Scheuer, Steven H., 1926-2014. (["Box 1, folder 4"])(n.y. Jun 21)[The Turning Point #11 Halsted Welles]. https://collections.library.yale.edu/catalog/17101430.