MLA

Crane, Hart, 1899-1932. Cowley, Peggy Baird to Anita Brenner. Box 5, folder 241. [1932?] Sep 28. https://collections.library.yale.edu/catalog/17155297.

APA, 6th edition

Crane, Hart, 1899-1932. (["Box 5, folder 241"])([1932?] Sep 28)[Cowley, Peggy Baird to Anita Brenner]. https://collections.library.yale.edu/catalog/17155297.