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Karlsorus n. gen. is proposed in this study as a large, smooth-shelled pentameride brachiopod of the family Pentameridae, based on Pentamerus gothlandicus Lebedev, 1892, from the Wenlock (Silurian) Slite beds of Gotland, Sweden. This species is transferred from Pentamerus to the new genus because of the combination of a Pentamerus-like shell shape and the development of a brachiophorium through fusion of the outer hinge plates in the middle portion, like a dorso-ventrally inversed cruralium. The first appearance of brachiophorium in pentamerids is in the late Wenlock, known also in Brooksina, Pentamerifera, and other related pentamerid genera, marking a significant stage in morphological transformation of dorsal internal structures, as part of the Silurian pentameride diversification in both level-bottom and reefal depositional environments. [ABSTRACT FROM AUTHOR]

Stegerhynchus was perhaps the most common rhynchonellide brachiopod in the Early Silurian (Llandovery) postextinction brachiopod fauna of North America. In shell morphology, it closely resembles the Late Ordovician rhynchonellide Rhynchotrema in having a rostrate shell posterior and simple, strong costae. It differs internally from Rhynchotrema primarily in having a much-reduced septalium (=cruralium). Superficially Stegerhynchus has a conservative, typically simple, rhynchonellide morphology, but detailed biometric analysis of large samples from the >400 m-thick Llandovery (mid-Aeronian to mid-Telychian) tropical carbonate succession of Anticosti Island reveals that the genus underwent significant evolutionary and ecophenotypic changes over about five million years. The shell length/width ratios of Stegerhynchus peneborealis from sediments of a low-energy, muddy substrate tend to be lower than those of S. deltolingulatus new species from high-energy, reef or inter-reef settings. A wider shell and hingeline probably had a greater stability on the soft seafloor. Also a wider shell appears to be associated with a larger (relative to shell size) sulcus size at the anterior margin. The changes in relative sulcus size either represent ecophenotypic variation in response to environmental conditions, or a random effect of evolutionary selection through time. Both multivariate and single-character analyses demonstrate that two important biometric features, the apical angle and shell flank rib number, separate all forms of Anticosti Island Stegerhynchus (middle Aeronian to middle Telychian) from the widely cited European species Stegerhynchus borealis (latest Telychian-Wenlock) from the type area of Gotland, Sweden. The temporal changes of these two characters are interpreted to be evolutionary modifications. [ABSTRACT FROM AUTHOR]

Examines the three types of Parastrophinella, Pentamerus reversus, one of the earlier Canadian brachiopod species named by Billings (1857) and based on specimens collected by James Richardson. Features of species; How species have developed; Where species have been discovered; Species excluded from the Parastrophinella family.