MLA

Ronnebeck, Arnold, 1885-1947. Däubler, Theodor. Box 1. 1921-1934, undated. https://collections.library.yale.edu/catalog/17170344.

APA, 6th edition

Ronnebeck, Arnold, 1885-1947. (["Box 1"])(1921-1934, undated)[Däubler, Theodor]. https://collections.library.yale.edu/catalog/17170344.