MLA

Stieglitz, Alfred, 1864-1946. Letters. Box 77, folder 1607-1609. 1941 Sep-Nov. https://collections.library.yale.edu/catalog/2043570.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 77, folder 1607-1609"])(1941 Sep-Nov)[Letters]. https://collections.library.yale.edu/catalog/2043570.