A Specimen of Cyclus has lately been acquired from the Carboniferous Limestone of St. Doulaghs, co. Dublin, which indicates a new species, though it is allied to several which have been described by Dr. Henry Woodward. The latter gave in 1894 a review of our knowledge of this curious little Crustacean genus, and his view that it is an Entomostracan and probably one of the Phyllopoda has been generally accepted, though more recently (1905) he has suggested that the members of this genus are but the larval stages of Coal-measure Limuloids.