The internal features of some Paleozoic rhynchonellid brachiopods

Abstract

The genera Lissopleura, Sphaerirhynchia, Pectorhyncha, Yanishewskiella, and Terebratuloidea have been investigated to elucidate their internal features and taxonomic relationships. Specimens of the type species of these genera were sectioned. Lissopleura remains slightly enigmatic in that the holotype of Lissopleura aequivalvis is thinner and has a less pronounced fold than most specimens in the collection, including the one sectioned by us. The holotype is probably immature and is within the range of variation of specimens from the type area. The internal features lead us to assign Lissopleura to the Trigonirhynchiidae. Sphaerirhynchia wilsoni has a short septalium without a cover plate and other features that place it in the Hebetoechiidae. Pectorhyncha obtusiplicata has a very thick shell and a septalium filled by a large, bilobed cardinal process. The genus has several features similar to Obturamentella, and is assigned to the Obturamentellidae. Yanishewskiella angulata, which is retained within the Tetracameridae, has a spondylium with lateral buttresses, and a septalium into which the medium septum projects. Terebratuloidea davidsoni has small dental plates, and is assigned to the Allorhynchidae.