MLA

Whitman, Walt, 1819-1892. Samuel Hollyer engraving. Box 1, folder 22. [1855?]. https://collections.library.yale.edu/catalog/2053656.

APA, 6th edition

Whitman, Walt, 1819-1892. (["Box 1, folder 22"])([1855?])[Samuel Hollyer engraving]. https://collections.library.yale.edu/catalog/2053656.