MLA

Pound, Ezra, 1885-1972. Fitzgerald, Robert. Box 16, folder 736. 1931-55. https://collections.library.yale.edu/catalog/17430535.

APA, 6th edition

Pound, Ezra, 1885-1972. (["Box 16, folder 736"])(1931-55)[Fitzgerald, Robert]. https://collections.library.yale.edu/catalog/17430535.