	Authors	Year	Title
	Alberti, Groos-Uffenorde & Streel	1974	The stratigraphical significance of the Protognathodus fauna from Stockum (Devonian/Carboniferous boundary, Rhenish Schiefergebirge). Newsletters on Stratigraphy, 3,4: 263-276, fig.1,2; Leiden.
	Paproth & Streel	1970	Correlations biostratigraphique pres de la limite Devonien/Carbonifère entre les facies littoroux ardennais et les facies bathyaux rhenans. Congr. Coll. Univ. Liège, 55: 365-398, pl.1-3, fig.1-3; Liège.