MLA

Lowenfels, Walter, 1897-1976. Selby, Hubert. Box 30, folder 617. 1956-1964, undated. https://collections.library.yale.edu/catalog/17174423.

APA, 6th edition

Lowenfels, Walter, 1897-1976. (["Box 30, folder 617"])(1956-1964, undated)[Selby, Hubert]. https://collections.library.yale.edu/catalog/17174423.