MLA

Stieglitz, Alfred, 1864-1946. Letters. Box 75, folder 1589-1590. 1940 Feb-Mar. https://collections.library.yale.edu/catalog/2043465.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 75, folder 1589-1590"])(1940 Feb-Mar)[Letters]. https://collections.library.yale.edu/catalog/2043465.