The diagnosis of the dinoflagellate cyst genusSarjeantiaHorowitz is revised so as to incorporate information on its cavation and method of excystment. Examination of the other microfossils (acritarchs, miospores and dinoflagellate cysts) present with the holotype in the type slide suggests a much younger date than that hitherto assigned to it, probably Middle Jurassic (upper Bathonian) rather than Upper Triassic.