MLA

Fitzgerald, Robert, 1910-1985. Lowell, Robert. Box 54, folder 1997. 1973. https://collections.library.yale.edu/catalog/17093658.

APA, 6th edition

Fitzgerald, Robert, 1910-1985. (["Box 54, folder 1997"])(1973)[Lowell, Robert]. https://collections.library.yale.edu/catalog/17093658.