The history of study of these dinoflagellates is reviewed and emended diagnoses are proposed for the generaCtenidodiniumandDichadogonyaulax.A new species,Dichadogonyaulax sellwoodii,is described and illustrated from the Bathonian of the Isle of Skye, Scotland. The new combinationDichadogonyaulax norrisii(Pocock, 1972) is proposed and it is considered that forms described by Gocht (1970) asCtenidodinium pachydermum(Deflandre, 1938) may in fact be'attributable to Pocock's species. The speciesCtenidodinium continuumGocht, 1970, is briefly discussed and other Jurassic species attributable to these two genera are listed.