MLA

Bahlmann, Anna Catherine, 1849-1916. Postcard albums. Box 6, folder 117-209a. 1904-19[12?], undated. https://collections.library.yale.edu/catalog/32459530.

APA, 6th edition

Bahlmann, Anna Catherine, 1849-1916. (["Box 6, folder 117-209a"])(1904-19[12?], undated)[Postcard albums]. https://collections.library.yale.edu/catalog/32459530.