@book{45856,
	author = {Wahlmann, G. P.},
	title = {Middle and Upper Ordovician symmetrical univalved mollusks (Monoplacophora and Bellerophontina) of the Cincinnati arch region},
	publisher = {U.S. G.P.O.},
	year = {1992.},
	series = {Geological Survey professional paper},
	address = {Washington}
}