MLA

Pound, Ezra, 1885-1972. Butts, Mary. Box 7, folder 309. 1932-34. https://collections.library.yale.edu/catalog/31908813.

APA, 6th edition

Pound, Ezra, 1885-1972. (["Box 7, folder 309"])(1932-34)[Butts, Mary]. https://collections.library.yale.edu/catalog/31908813.