Article: The Silurian brachiopod Stegerhynchus
The brachiopod Stegerhynchus Foerste, 1909 occurs in Silurian strata in Canada, the U.S.A., the U.S.S.R., Gotland, and the United Kingdom. Review of the literature shows that Rhynchonella whitii praecursor Hall, 1863 is the true type species of Stegerhynchus. Although Stegerhynchus and Ferganella Nikiforova, 1937 are morphologically very similar, they can be separated because Stegerhynchus has an open notothyrial cavity that houses an elongate cardinal process based on the notothyrial platform, whereas Ferganella has a septal process extending anteriorly from the posteriorly conjunct hinge plates. The septal process joins the cardinal process distally. Stegerhynchus seems to be most common in Wenlock and Ludlow strata and less common in Llandovery and Pridoli strata. Ferganella appears to be of Pridoli/Lower Devonian age. Species such as S. borealis and S. diodonta are relatively long-ranging while other species such as S. angaciensis have a relatively short range. S. borealis is relatively common in the Upper Silurian Read Bay Formation of the Canadian Arctic islands, whereas S. angaciensis is relatively rare, being found only at the base of member C of the Read Bay Formation on the east coast of Cornwallis Island.