MLA

Cassirer, Ernst, 1874-1945. Research notes. Box 31, folder 599-605. n.d.. https://collections.library.yale.edu/catalog/17274603.

APA, 6th edition

Cassirer, Ernst, 1874-1945. (["Box 31, folder 599-605"])(n.d.)[Research notes]. https://collections.library.yale.edu/catalog/17274603.