The Early Silurian brachiopod Pentameroides from the Hudson Bay Lowlands, Ontario: Discussion

Abstract

We are indebted to Jin and Copper for demonstrating that Whiteaves' (1904, 1906) Reticularia septentrionalis, and Meristina? expansa belong to a single pentameroid species, which we would place in Reveroides, and that it is identical to Boucot and Johnson's (1979) Sapelnikovia nor$ordi. Their documentation of the internal features is helpful in considering the affinities of the form. Jin and Copper synonymize Sapelnikov's (1976) Reveroides (= Sapelnikovia) with Pentameroides (in the abstract and text of their paper they indicate uncertainty about this, employing the words probable synonym and a junior synonym, but in their synonomy for Pentameroides septentrionalis they actually synonymize the form in question). They conclude that the nature of the brachial structures in R. septentrionalis is similar enough to those illustrated by Sapelnikov (1961) for the forms later placed in Reveroides to make a congeneric assignment necessary. The possibility that the similar brachial structures are probably family-level, rather than generic, features was evidently not considered. They justify synonymizing Reveroides (= Sapelnikovia) with Pentameroides by means of alleged, common external form. Jin and Copper comment that collections available to them from elsewhere include non-trilobate, even bisulcate, specimens of Pentameroides and that some of the material from Whiteaves' localities actually show trilobation. Their figures (Pl. 1 , figs. 1-5) of R. septentrionalis lacking prominent bilobation also lack trilobate form and are far more globose than is the case with either Pentamerus trilobatus, the type species of Pentamerus, or Pentameroides subrectus, the type species of Pentameroides. Jin and Copper question the value of trilobation as an essential character in diagnosing Pentameroides, employing both non-bisulcate specimens of R. septentrionalis and Pentameroides material (unillustrated by them) from the Fossil Hill Formation on Manitoulin Island. It should be remembered that Schuchert and Cooper (1932) set up Pentameroides because of its externally homeomorphous similarity, trilobate on average, to Pentamerus (type species Pentamerus trilobatus). It is no accident that the average forms of both Pentamerus sensu strictu and of Pentameroides sensu strictu are trilobate, based on abundant mate-