MLA

Pound, Ezra, 1885-1972. Williams, William Carlos. Box 55, folder 2516-2528. [1910]-60. https://collections.library.yale.edu/catalog/2000068.

APA, 6th edition

Pound, Ezra, 1885-1972. (["Box 55, folder 2516-2528"])([1910]-60)[Williams, William Carlos]. https://collections.library.yale.edu/catalog/2000068.