MLA

Koch, Frederick R. (Frederick Robinson). Music/Totentanz. Box 345, folder 2046. n.d.. https://collections.library.yale.edu/catalog/2043677.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 345, folder 2046"])(n.d.)[Music/Totentanz]. https://collections.library.yale.edu/catalog/2043677.