MLA

O'Neill, Eugene, 1888-1953. From Oona Chaplin. Box 10, folder 189. [1941 Sep]. https://collections.library.yale.edu/catalog/17155206.

APA, 6th edition

O'Neill, Eugene, 1888-1953. (["Box 10, folder 189"])([1941 Sep])[From Oona Chaplin]. https://collections.library.yale.edu/catalog/17155206.