MLA

Stieglitz, Alfred, 1864-1946. Letters. Box 87, folder 1738-1740. 1931 Jun-Jul. https://collections.library.yale.edu/catalog/2040488.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 87, folder 1738-1740"])(1931 Jun-Jul)[Letters]. https://collections.library.yale.edu/catalog/2040488.