Author: Welter, O.A., 1910.:
Title: Die Pharetronen aus dem Essener Grünsand.
Description: Verh. Nat. Ver. Preuss. Rheinl. Westf., 67: pp. 1-82, 57 figs. on 3 double-page pls., 12 figs. in text. Wrs. - Calcispongia, Lower Cretaceous.

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