Pachythrissops is an extinct genus of ray-finned fish. It contains two species, P. laevis from the Purbeckian of England and P. propterus from the Tithonian of Germany. A third species, P. vectensis, has been reassigned to the elopiform genus Arratiaelops. Pachythrissops is often regarded as one of the most primitive members of the order Ichthyodectiformes; however, a phylogenetic analysis by Cavin et al. (2013) placed it and the related genus Ascalabothrissops outside the group.