MLA

Stieglitz, Alfred, 1864-1946. Letters. Box 91, folder 1806-1812. 1940 Jun-Nov. https://collections.library.yale.edu/catalog/2042819.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 91, folder 1806-1812"])(1940 Jun-Nov)[Letters]. https://collections.library.yale.edu/catalog/2042819.