Illustrations showing the overlap of the outline morpho-spaces of five species of Ilyocypris that have living or Quaternary representatives in eastern Inner Mongolia. All outlines have been standardised for equal surface area, rotated with the antero-ventral and the postero-ventral parts resting horizontally, and with the geometric centres set at (0, 0) A outlines of 42 valves B mean outlines of the five species. Arrows indicate areas showing relatively large inter-species variability, i.e., the postero-dorsal‒posterior and the postero-ventral areas C principal Component Analysis (PCA) biplot of 42 valves based on their outline data. Coloured shaded areas indicate the morpho-spaces of the five species, cast on the two-dimensional space defined by PCA axis 1 and 2.