MLA

Koch, Frederick R. (Frederick Robinson). Music/Frottola. Box 342, folder 2009. [mid 1890s]. https://collections.library.yale.edu/catalog/2043649.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 342, folder 2009"])([mid 1890s])[Music/Frottola]. https://collections.library.yale.edu/catalog/2043649.