FIGURES 17–20 in Gomphonema beaugerianum, a new Gomphonema species (Bacillariophyta) found in a historic William Smith sample from the Auvergne (France)

FIGURES 17–20. Gomphonema beaugerianum Van de Vijver, sp. nov. LM and SEM images taken from the holotype sample (BR-4847, Lac de Guéry, Auvergne, France, sample W. Smith). 17. SEM external view of an entire valve in oblique view showing the valve mantle. 18. SEM external detail of the central area showing the isolated pore and the depressed areolae with the reniform siliceous flaps. Note also the shallow depressions in the axial area. 19. SEM internal view of an entire valve. 26. SEM internal detail of the central area showing the slit-like isolated pore and the hooked central raphe endings. Note the absence of silica struts separating the areolae. Scale bars = 10 µm (Figs 17–19) = 1 µm (Fig. 20).