MLA

Wilder, Thornton, 1897-1975. Wilder, Catherine Dix. Box 3, folder 67-70. 1939-75, n.d.. https://collections.library.yale.edu/catalog/16587313.

APA, 6th edition

Wilder, Thornton, 1897-1975. (["Box 3, folder 67-70"])(1939-75, n.d.)[Wilder, Catherine Dix]. https://collections.library.yale.edu/catalog/16587313.