MLA

Byron, Robert, 1905-1941. Notebooks. Box 23, folder 436-437. undated. https://collections.library.yale.edu/catalog/2107231.

APA, 6th edition

Byron, Robert, 1905-1941. (["Box 23, folder 436-437"])(undated)[Notebooks]. https://collections.library.yale.edu/catalog/2107231.