MLA

Marshall, Margaret, 1900-1974. Bedford, Sybille. Box 5, folder 145. 1968-72. https://collections.library.yale.edu/catalog/17029485.

APA, 6th edition

Marshall, Margaret, 1900-1974. (["Box 5, folder 145"])(1968-72)[Bedford, Sybille]. https://collections.library.yale.edu/catalog/17029485.