MLA

Beinecke, Edwin J. (Edwin John), 1886-1970. Stevenson, Robert Louis. Box 64, folder 1487-1492. 1852-1894, undated. https://collections.library.yale.edu/catalog/2032271.

APA, 6th edition

Beinecke, Edwin J. (Edwin John), 1886-1970. (["Box 64, folder 1487-1492"])(1852-1894, undated)[Stevenson, Robert Louis]. https://collections.library.yale.edu/catalog/2032271.