MLA

Pound, Ezra, 1885-1972. Bowen, Catherine Drinker. Box 5, folder 231. 1958. https://collections.library.yale.edu/catalog/17122526.

APA, 6th edition

Pound, Ezra, 1885-1972. (["Box 5, folder 231"])(1958)[Bowen, Catherine Drinker]. https://collections.library.yale.edu/catalog/17122526.