MLA

Stieglitz, Alfred, 1864-1946. Letters. Box 91, folder 1804-1805. 1940 Feb-Mar. https://collections.library.yale.edu/catalog/2042817.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 91, folder 1804-1805"])(1940 Feb-Mar)[Letters]. https://collections.library.yale.edu/catalog/2042817.