MLA

Byron, Robert, 1905-1941. Stokes, Adrian Durham. Box 14, folder 309. undated. https://collections.library.yale.edu/catalog/16603520.

APA, 6th edition

Byron, Robert, 1905-1941. (["Box 14, folder 309"])(undated)[Stokes, Adrian Durham]. https://collections.library.yale.edu/catalog/16603520.