MLA

Koch, Frederick R. (Frederick Robinson). Music/Songs and piano music. Box 109, folder 1451. [1888?]-91, n.d.. https://collections.library.yale.edu/catalog/2043922.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 109, folder 1451"])([1888?]-91, n.d.)[Music/Songs and piano music]. https://collections.library.yale.edu/catalog/2043922.