MLA

Wharton, Edith, 1862-1937. Brownell, William Carey. Box 23, folder 727. 1909-26. https://collections.library.yale.edu/catalog/16782183.

APA, 6th edition

Wharton, Edith, 1862-1937. (["Box 23, folder 727"])(1909-26)[Brownell, William Carey]. https://collections.library.yale.edu/catalog/16782183.