On The Lower Carboniferous Corals : Rhopalolasma Bradbournense (Wilmore) And Rhopalolasma Rylstonense Sp. Nov.

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Abstract
Summary Descriptions are given of Rhopalolasma bradbournense (Wilmore) and R. rylstonense sp. nov., two species of corals which occur in the Middle Viséan of the Carboniferous Central Province. The difference between them is not expressed in the ontogeny of either and is considered to be neither palingenetic nor coenogenetic variation. The forms belong to the same species-plexus as R. tachyblastum Hudson and R. sympecta Hudson from the Lower Viséan, and differences between these earlier and later forms are correlated with a change in the upward, relative to the outward, growth-rate of the corallum. The occurrence of a few but abnormally lengthy cylindrical individuals of R. rylstonense and R. bradbournense is also attributed to a change in the differential growth-rate of the corallum. I. Introduction Numerous small zaphrentoid corals characterized by a stereocolumn 1 and occurring in the zaphrentid-phase faunas of the Carboniferous have been listed by various authors under the genus Densiphyllum Dybowski. Those forms which occur in the Middle Viséan are usually named D. bradbournense Vaughan or D. rushianum Vaughan. The taxonomy of the former species, which has never been adequately described, is involved : in this paper the author redescribes the species and shows that it belongs to the genus Rhopalolasma Hudson. II. Generic Diagnoses Genus Densiphyllum Dybowski 1873 The genolectotype of the genus Densiphyllum Dybowski 1873 is D. thomsoni Dybowski 1873, a coral from zone 4 (Schmidt 1858) of the Silurian of Herkull, Esthonia (see Lang, Smith and Thomas 1940, p. 49). This species, according to Dybowski (1873,

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