A few years ago Mr. Carruthers described an aberrant coral, Cryptophyllum hibernicum, from the Lower Carboniferous of Bundoran, Donegal. Cryptophyllum occurred in the Lower Calp shales, which are considered to be about at the horizon of Vaughan's C2 to S1 beds. Another aberrant genus, Heptaphyllum, also from the north-west of Ireland—Lower Carboniferous shales, Sligo—forms the subject of this paper. Cryptophyllum is remarkable, first for the manner in which the earlier major septa appear—irregularly, and nearly simultaneously, instead of regularly, and in consecutive pairs, as is typical for Rugose Corals; and also in the development of only five septa instead of the normal six in the earliest growth stages. Heptaphyllum, as its name implies, develops seven septa in the young corallum. It resembles Cryptophyllum in having an early aseptate corallum, and in the way in which the earlier septa appear.