MLA

Fitzgerald, Robert, 1910-1985. Fitzgerald, Robert David. Box 12, folder 461. 1968 Oct 19. https://collections.library.yale.edu/catalog/17427372.

APA, 6th edition

Fitzgerald, Robert, 1910-1985. (["Box 12, folder 461"])(1968 Oct 19)[Fitzgerald, Robert David]. https://collections.library.yale.edu/catalog/17427372.