Modalities of phyletic evolution of some Neodevonian phacopines (trilobites) under environmental constraints.

Traditionally, the Late Devonian phacopines with reduced eyed, from deeper- water external platforms are integrated in the single taxon Cryphops, despi te its discontinuous distribution in time. A new interpretation of phyletic relationships is proposed here, taking into account ventral cephalic chara cters that have hitherto not been considered. In this model, different line s leading to the "Cryphops" morphotype derived repeatedly and independently from the ancestral Phacops root stock by iterative evolution.