Article: Revision of the Ordovician carpoid family Iowacystidae
Newly discovered specimens and re-evaluation of previous evidence indicate a much closer relation between the solutan carpoids Belemnocystites, Myeinocystites, Scalenocystites, and lowacystis than was previously suspected. Comparative studies of all known species, including observations on the ontogeny of S. strimplei Kolata and I. sagittaria Thomas and Ladd, show that numerous thecal and steleal structures are homologous. In light of the obvious affinity shown by these carpoids, it is proposed that the Family Belemnocystitidae (Belemnocystites, Myeinocystites, and Scalenocystites) be synonymized with the Family lowacystidae (lowacystis). The likely synonymy of Belemnocystites and Myeinocystites is suggested from a re-examination of the holotype of B. wetherbyi Miller and Gurley. All species are redescribed and illustrated. A new species, M. crossmani, is described from the Trentonian (Caradocian) Dunleith Formation (Galena Group) of Illinois and Iowa. The dorso-ventrally depressed theca, high degree of bilateral symmetry, anterior mouth, and flexible, caudal appendage suggest that the iowacystids were vagrant bottom-dwelling echinoderms that were adapted to a browsing mode of life. They very likely lived with the oral opening and ambulacral groove facing the substrate. The iowacystids inhabited warm, shallow epeiric seas in environments characterized by relatively quiet deposition of carbonate sediments.