. Bulletins of American paleontology. Devonian Rugose Corals of Iowa: Sorauf 73 ence of normal, sloping dissepiments internal to the horseshoe forms, as proposed by Birenheide (1978). There are recognizable groups of species within the massive colonial phillipsastreids, and to ignore these is potentially to ignore the evolutionary development of these corals and also obscure the biostratigraphic value of them. These groups can be summarized as follows: 1. There is a conservative group of corals which comprises species that do not show marked uniformity in their development of horseshoe dissepi
. Bulletins of American paleontology. Devonian Rugose Corals of Iowa: Sorauf 73 ence of normal, sloping dissepiments internal to the horseshoe forms, as proposed by Birenheide (1978). There are recognizable groups of species within the massive colonial phillipsastreids, and to ignore these is potentially to ignore the evolutionary development of these corals and also obscure the biostratigraphic value of them. These groups can be summarized as follows: 1. There is a conservative group of corals which comprises species that do not show marked uniformity in their development of horseshoe dissepiments. Some species may show little differentiation of the inner dis- sepiments, but all have somewhat everted calices, all have fans of septal trabeculae, all have the tendency to have long septa that are dilated at the inner border of the dissepimentarium, and all have a pseudocerioid to thamnasterioid colonial form. All species are vari- able, thus it is an error to use one individual corallite or one colony as the basis for acceptance or rejection of species or genus assignment. This group of species is typified by Phillipsastrea hetmahi. itself a highly variable species. Closely related species with pseudo- cerioid colonial form and little or no development of specialized dissepiments, but with fanning septal tra- beculae, are placed in Frechastraea. 2. There is a group of species that are advanced in that they have a complete tube or sleeve of uniform horseshoe-shaped dissepiments and marked septal di- lation. They generally lack internal dissepiments and do not have the pseudocerioid colonial form, rather, they may have an aphroid colonial form, and have cal- icinal prominences around the tabularium. This group of species also generally have relatively sinall diameter corallites, in the 3-8 mm range. This group of species is typified by Pachyphyllum woodmani. 3. There is another group of advanced species, few- er in number, but distinctive in appearance because of the pr
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