Abstract
A specimen was discovered in the Ehrenberg Collection at BHUPM that can serve as lectotype of Pinnularia gastrum, the type species of Placoneis Mereschkowsky. Previously, Cox was unable to find an authentic specimen in the Ehrenberg Collection and therefore proposed to conserve the binomial with a Donkin specimen at the BM. The usefulness of conserving names to settle uncertainties of typification is discussed. In addition, Pinnularia placentula, a species morphologically similar to P. gastrum, is lectotypified with Ehrenberg's original drawing. Since the type specimen is lost, Cox's proposed neotype can serve as epitype.