MLA

Barnard, Mary, 1909-2001. Pound, Ezra. Box 12. 1933-1950. https://collections.library.yale.edu/catalog/17430066.

APA, 6th edition

Barnard, Mary, 1909-2001. (["Box 12"])(1933-1950)[Pound, Ezra]. https://collections.library.yale.edu/catalog/17430066.