FIGURES 219–225: SEM micrographs. Figs 219–222. Hippodonta abunda (type material). Fig. 219. External view of entire valve. Terminal pores of raphe are simple linear depressions. Fig. 220. External view of complete frustule showing broad, unornamented girdle. Fig. 221. Internal view of entire valve. Striae positioned in shallow depressions, helictoglossae in line with raphe slits. Fig. 222. Close-up of one half of valve, internal view. Lineolae covered by quite prominent elliptical volae. Fig. 223. Hippodonta rostratoides (type material). External view of entire valve. Lineolae quite prominent. Terminal pores of raphe slightly deflected towards one valve side. Fig. 224. Hippodonta affinis (type material). External view of entire valve. Lineolae narrow but long. Terminal pores of raphe simple linear. Fig. 225. Hippodonta exigua (type material). External view of entire valve. Lineolae weakly pronounced, short. Terminal pores of raphe slightly deflected towards one valve side. Scale bars in Figs 219, 223, 224 = 5 µm; Fig. 220 = 2 µm; Fig. 221 = 6 µm; Fig. 222 = 3 µm; Fig. 225 = 4 µm.