MLA

Marsh, Othniel Charles, 1831-1899. Beck, William. Box 3, folder 81. 1885-1886. https://collections.library.yale.edu/catalog/32209963.

APA, 6th edition

Marsh, Othniel Charles, 1831-1899. (["Box 3, folder 81"])(1885-1886)[Beck, William]. https://collections.library.yale.edu/catalog/32209963.