Books by Hermann W. Pfefferkorn:
Books in the extended shelves:
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Pfefferkorn, Hermann W.: Pennsylvanian tree fern compressions (Illinois State Geological Survey, 1976), also by Illinois State Geological Survey and Illinois. Dept. of Registration and Education (page images at HathiTrust)- Pfefferkorn, Hermann W.: Some fern-like fructifications and their spores from the Mazon Creek compression flora of Illinois (Pennsylvanian) (Illinois State Geological Survey, 1971), also by Tom Lee Phillips and Russel A. Peppers (page images at HathiTrust)
Find more by Hermann W. Pfefferkorn at your library, or elsewhere.