MLA

Hilles, Frederick W. (Frederick Whiley), 1900-1975. Carlyle, Thomas. Box 21, folder 602. undated. https://collections.library.yale.edu/catalog/16048269.

APA, 6th edition

Hilles, Frederick W. (Frederick Whiley), 1900-1975. (["Box 21, folder 602"])(undated)[Carlyle, Thomas]. https://collections.library.yale.edu/catalog/16048269.