MLA

Thayer, Scofield, 1889-1982. Williams, William Carlos. Box 44, folder 1265a. 1920-26. https://collections.library.yale.edu/catalog/17142324.

APA, 6th edition

Thayer, Scofield, 1889-1982. (["Box 44, folder 1265a"])(1920-26)[Williams, William Carlos]. https://collections.library.yale.edu/catalog/17142324.