MLA

Wilson, Elena, 1906-1979. Mumm, Hermann, contract for marriage with Olga Struve, copies. Box 30, folder 731. n.d.. https://collections.library.yale.edu/catalog/17197610.

APA, 6th edition

Wilson, Elena, 1906-1979. (["Box 30, folder 731"])(n.d.)[Mumm, Hermann, contract for marriage with Olga Struve, copies]. https://collections.library.yale.edu/catalog/17197610.