MLA

Norton, Caroline Sheridan, 1808-1877. ALS to Dr. Edward Craven Hawtrey, Richmond, England. Box 1, folder 9. [1840?] May 18. https://collections.library.yale.edu/catalog/16495507.

APA, 6th edition

Norton, Caroline Sheridan, 1808-1877. (["Box 1, folder 9"])([1840?] May 18)[ALS to Dr. Edward Craven Hawtrey, Richmond, England]. https://collections.library.yale.edu/catalog/16495507.