MLA

Simpson, Randolph Linsly, 1927-1992. Un-numbered Items. Box 10, folder 312-313. undated. https://collections.library.yale.edu/catalog/17028112.

APA, 6th edition

Simpson, Randolph Linsly, 1927-1992. (["Box 10, folder 312-313"])(undated)[Un-numbered Items]. https://collections.library.yale.edu/catalog/17028112.