Parallel evolution of many skeletal characteristics seems to exist within the present framework of archaeocyathid systematics. The number of rows of interseptal pores on the inner and outer walls is reduced in younger species within the Ajacicyathidae, Erbocyathidae, and Coscinocyathidae. Thickening of the inner wall accompanied by development of pore canals appears in younger species of the Ethmophyllidae and Erbocyathidae of the Ajacicyathina and in Coscinocyathellus of the Coscinocyathina. The porosity of the septum decreases in younger species of some genera of the Erbocyathidae, Ethmophyllidae and Tumulocyathidae. Colonial species develop in the younger evolutionary stages of several apparently unrelated genera. Species with simple outer walls are most common in older deposits in all environments. Species with additional outer wall membranes are most common in younger deposits in all environments. Species with reticulate outer walls are common only in eugeosynclinal deposits associated with abundant evidence of effusive volcanic activity. Ontogenetic studies show that morphologic features of suprageneric value do not always appear in the same sequence even in related genera. Within the Lenocyachidae, a septum between the inner and outer walls in Kotuyicyathus and Lenocyathus appears before the outer wall becomes complex, but in Jakutocyathus, the outer wall becomes complex first.