The bryozoan genus Evactinopora was first named by Meek and Worthen (1865) with E. radiata as type species, based on a silicified fossil from the Lower Carboniferous (=Mississippian) Keokuk Limestone, collected at an unknown location in Missouri. E. radiata is an 8-rayed colony with thin rays. Subsequently, Meek and Worthen described E. sexradiata for a 6-rayed colony and E. grandis for a much larger 4-rayed colony. Instead of illustrating a 6-rayed specimen for E. sexradiata, they illustrated a 5-rayed specimen, a discrepancy pointed out by Ulrich (1884). In 1890, Ulrich described E. quinqueradiata for colonies with five vanes. These species of Evactinopora have not been revised since then and the worth of the proposed species based on the number of vanes in the colony has not been evaluated. Weller (1909) presented data for a collection of colonies showing variation from four to nine vanes, but did not propose new species names for the more multi-rayed specimens. In their book Index Fossils of North America, Shimer and Shrock list only E. radiata and E. grandis as species.
Meek & Worthen (1865) 8 rays E. radiata Meek & Worthen (1868) 6 rays E. sexradiata Ulrich (1890) 5 rays E. quinqueradiata Meek & Worthen (1868) 4 rays E. grandis
Several other fossils have been described as species of Evactinopora from the continents of Europe and Australia. Two relatively recent publications have illustrated specimens of Evactinopora in Europe: Morozova (1981) reported Evactinopora from European Russia and Ernst (2004) reported Evactinopora from Germany. The E. sp. of Ernst (2004) is similar to E. radiata of North America, but E. incerta of Morozova (1981) is known only from small cross sections that do not show the colony form. At this time, there are no reliable reports of the genus in England or Ireland.
Morozova (1981) ? rays E. incerta Russia Ernst (2004) 5 rays E. sp. Germany
Specimens in Australia were the first non-American fossils referred to the genus. Hudleston (1883) described E. crucialis for a 4-rayed specimen very similar to E. grandis and E. dendroidea for a colony with a round cross-section that is very different from type Evactinopora. Both were collected from Western Australia near Shark Bay, but they come from strata of Permian age. E. dendroidea is unrelated to Evactinopora and was reclassified as Hexagonella dendroidea by Hinde (1890). E. crucialis was reclassified by Wass (1967) as Evactinostella crucialis. The much younger age of this fossil raises doubts about its relationship to Evactinopora.
Hudleston (1883) no rays E. dendroidea Australia Hudleston (1883) 4 rays E. crucialis Australia Crockford (1947) 4 rays E. trifoliata Australia Crockford (1947) 4 rays E. irregularis Australia Campbell & Engel (1963) 8 rays E. tenuiradiata Australia
A few other fossils were originally described as species of Evactinopora, but are entirely unrelated to Evactinopora. In 1927, Warren proposed two new species in the genus Evactinopora for specimens of a different morphology having long slender rays with circular cross-section, collected in the Banff area of Canada. His species are unlike Evactinopora radiata and were later transferred to a new genus Macgowanella (Nelson and Bolton, 1980). This genus is similar to the genera Palaeocoryne Duncan and Jenkins, 1869, and Claviradix Ferguson, 1961, fossils described for English specimens that Bancroft (1988) showed to be unrelated to Evactinopora. Bancroft (1988) showed that they are outgrowths of the colonies of fenestellid bryozoans. This group also includes an English fossil originally described as Evactinopora castletoniensis by Barnes (1903).
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