MLA

Koch, Frederick R. (Frederick Robinson). Caricature of Liszt: in pencil. Box 26, folder 576. [late 19th c?]. https://collections.library.yale.edu/catalog/2018100.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 26, folder 576"])([late 19th c?])[Caricature of Liszt: in pencil]. https://collections.library.yale.edu/catalog/2018100.