A Study of the Middle Pennsylvanian Flora Found in Kansas Coal Balls, Doctoral Dissertation of David A. Otto, Ph.D, 1967, Box: 1, Volume: 1. Study of the Middle Pennsylvanian Flora Found in Kansas Coal Balls, RH MS 1259. University of Kansas. Kenneth Spencer Research Library. https://archives.lib.ku.edu/repositories/3/archival_objects/57591 Accessed April 22, 2025.