	Authors	Year	Title
	Hodson	1957	Marker horizons in the Namurian of Britain, Ireland, Belgium and Western Germany. Association pour l'Etude de Paléontologie et de la Stratigraphie Houillères, Publication 24: 1-26, fig.1-3, pl.1-7; Bruxelles.
	Moore	1946	The Carboniferous goniatite genera Girtyoceras and Eumorphoceras. Proceedings of the Yorkshire Geological Society, 25: 387-445, 31 figs., pl.22-27; Wakefield.