MLA

Leoncavallo, Ruggiero, 1858-1919. Unidentified. Box 10, folder 307. [1892]. https://collections.library.yale.edu/catalog/16666543.

APA, 6th edition

Leoncavallo, Ruggiero, 1858-1919. (["Box 10, folder 307"])([1892])[Unidentified]. https://collections.library.yale.edu/catalog/16666543.