CERATOPEAUlrich, 1911, from the Lower Ordovician of North America, Greenland, and Scotland, is one of a few gastropod genera that was established on the calcareous operculum and not the shell. The operculum is commonly found disassociated, and for many years the nature of the shell itself was unknown (Yochelson, 1975). Yochelson and Bridge (1957, pl. 38, figs. 8–9) illustrated an artificial association of C. unguis with its presumed shell made years earlier by Ulrich and Bridge (Yochelson, written commun.). However, the basal part of the shell is not present. Only one life association of the...

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