MLA

Sully, Alfred, 1821-1879. Correspondence. Box 1, folder 20. 1864. https://collections.library.yale.edu/catalog/16703590.

APA, 6th edition

Sully, Alfred, 1821-1879. (["Box 1, folder 20"])(1864)[Correspondence]. https://collections.library.yale.edu/catalog/16703590.