MLA

Zilboorg, James, 1892-1968. "P" general. Box 3, folder 45. undated. https://collections.library.yale.edu/catalog/17096137.

APA, 6th edition

Zilboorg, James, 1892-1968. (["Box 3, folder 45"])(undated)["P" general]. https://collections.library.yale.edu/catalog/17096137.