MLA

Carson, Rachel, 1907-1964. Free, Ann Cottrell. "Rachel Carson, 1907-1964." Defenders of Wildlife News Bulletin. Box 112, folder 2186. 1964 May. https://collections.library.yale.edu/catalog/17145215.

APA, 6th edition

Carson, Rachel, 1907-1964. (["Box 112, folder 2186"])(1964 May)[Free, Ann Cottrell. "Rachel Carson, 1907-1964." Defenders of Wildlife News Bulletin]. https://collections.library.yale.edu/catalog/17145215.