MLA

Stevenson, Robert Louis, 1850-1894. Documents relating to report that Robert Louis Stevenson had an illegitimate son. Box 2, folder 56. 1923-1925, undated. https://collections.library.yale.edu/catalog/16618678.

APA, 6th edition

Stevenson, Robert Louis, 1850-1894. (["Box 2, folder 56"])(1923-1925, undated)[Documents relating to report that Robert Louis Stevenson had an illegitimate son]. https://collections.library.yale.edu/catalog/16618678.