MLA

Hughes, Langston, 1902-1967. Douglass, Frederick. Box 19, folder 250-251. 1875-1978. https://collections.library.yale.edu/catalog/16207032.

APA, 6th edition

Hughes, Langston, 1902-1967. (["Box 19, folder 250-251"])(1875-1978)[Douglass, Frederick]. https://collections.library.yale.edu/catalog/16207032.