Brachiopod genus Lissocoelina Schuchert and Cooper, 1931, type species Pentamerus pergibbosus Hall and Whitfield, 1875, contrary to the condition implicit in its name, bears low radial plications anteriorly. It may be distinguished from true Conchidium and its homeomorphs by the form of the valves. Examination of Pentamerus pesovis Whitfield, Conchidium obsoletum Hall and Clarke, and C. occidentalis (Hall) leads to the conclusion that the last is a senior synonym inclusive of the other two. Conchidium occidentalis is made type species of a new genus Plicocoelina, a homeomorph of Lissocoelina bearing internal structures like those of Conchidium biloculare.

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