MLA

Thoreau, Henry David, 1817-1862. Printed ephemera. Box 1, folder 15. 1938, n.d.. https://collections.library.yale.edu/catalog/2056836.

APA, 6th edition

Thoreau, Henry David, 1817-1862. (["Box 1, folder 15"])(1938, n.d.)[Printed ephemera]. https://collections.library.yale.edu/catalog/2056836.