Fig. 17

Bivariate plots of conch parameters and septal spacing (of the last half volution) in the family Prionoceratidae (grey background dots represent the entire sample). A, D, G, J, M Conch width index (ww/dm) and septal spaces. B, E, H, K, N Whorl width index (ww/wh) and septal spaces. C, F, I, L, O Whorl expansion rate (WER) and septal spaces. A–C All representatives. D–F Late Tournaisian assemblage. G–I Early Tournaisian assemblage. J–L Late Famennian assemblage. M–O Middle Famennian assemblage