MLA

Simpson, Evelyn Mary Spearing, 1885-1963. Wasson, R. Gordon. Box 3, folder 82. 1960 Aug 29. https://collections.library.yale.edu/catalog/16828717.

APA, 6th edition

Simpson, Evelyn Mary Spearing, 1885-1963. (["Box 3, folder 82"])(1960 Aug 29)[Wasson, R. Gordon]. https://collections.library.yale.edu/catalog/16828717.