These are corals in which the septa are arranged in cycles of four. Both
solitary and colonial forms occur, and they are found only in rocks of
Paleozoic age. Rugose corals are abundant in many of the Paleozoic
formations of Texas, and two of the more typical forms
(_Lophophyllidium_ and _Caninia_) are illustrated in Plate 15. Members
of this order have been placed in the subclass Tetracoralla of older
classifications.