MLA

Pound, Ezra, 1885-1972. Duncan, Ronald Frederick Henry. Box 14, folder 628-640. 1936-68. https://collections.library.yale.edu/catalog/17122552.

APA, 6th edition

Pound, Ezra, 1885-1972. (["Box 14, folder 628-640"])(1936-68)[Duncan, Ronald Frederick Henry]. https://collections.library.yale.edu/catalog/17122552.