Abstract

The genus Coryellina has a small spine on the posterior surface of the valve that assumes a continuously higher position in progressively younger specimens. The validity of the assumption that the position of the spine can be used in broad stratigraphic determination is supported by precise measurement of Permian, Pennsylvanian and Mississippian specimens. Published data mostly from Russia on Upper Devonian and Lower Carboniferous species of Coryellina, and on Selebratina, a closely related if not synonymous genus of Middle and Late Devonian age, support this hypothesis. Linevella Chizhova, 1959, is considered a possible junior synonym of Coryellina. Coryellina is demonstrated to be dimorphic, and is therefore tentatively assigned to the family Primitiopsidae. A junior homonym is recorded but not renamed. One new species, Coryellina intermedia, is described, and a second new species is illustrated but not named.

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