MLA

Nicholls, Norton, 1741?-1809. Duchess di Castelpagano to Norton Nicholls. n.p. Concerns her co-author Wurmbrand. Box 2, folder 145. 1772 May 26. https://collections.library.yale.edu/catalog/17439942.

APA, 6th edition

Nicholls, Norton, 1741?-1809. (["Box 2, folder 145"])(1772 May 26)[Duchess di Castelpagano to Norton Nicholls. n.p. Concerns her co-author Wurmbrand]. https://collections.library.yale.edu/catalog/17439942.