MLA

Wharton, Edith, 1862-1937. Fullerton, William Morton. Box 25, folder 774. [1907] Oct 19. https://collections.library.yale.edu/catalog/10938113.

APA, 6th edition

Wharton, Edith, 1862-1937. (["Box 25, folder 774"])([1907] Oct 19)[Fullerton, William Morton]. https://collections.library.yale.edu/catalog/10938113.