MLA

Henri, Robert, 1865-1929. Dunlap, Helena. Box 3, folder 78. 1917. https://collections.library.yale.edu/catalog/17029566.

APA, 6th edition

Henri, Robert, 1865-1929. (["Box 3, folder 78"])(1917)[Dunlap, Helena]. https://collections.library.yale.edu/catalog/17029566.