MLA

Lewis, Sinclair, 1885-1951. Derleth, August William. Box 46, folder 482. [1937-1940]. https://collections.library.yale.edu/catalog/17116539.

APA, 6th edition

Lewis, Sinclair, 1885-1951. (["Box 46, folder 482"])([1937-1940])[Derleth, August William]. https://collections.library.yale.edu/catalog/17116539.