A homoeomorph of the articulate brachiopod Dicoelosia from the Upper Ordovician Hulterstad fauna of Öland, Sweden

The morphology of Dicoelosia (syn. Bilobites Quenstedt) is compared with other small punctate orthides of bilobed outline ascribed to the Dicoelosiidae, and in particular with Orthis cor Wiman, known only from loose blocks of Late Ordovician (Ashgill) age at Hulterstad on Öland. Despite the external similarities, the cardinalia in particular bear little resemblance to those of Dicoelosia. The recognition of fine surface pitting suggests a relationship to the Saukrodictyidae, which is confirmed by the morphology of the shell interiors. Wiman's species is redescribed and placed in a new genus, Hulterstadia, of this hitherto monotypic family. The generic characters of Saukrodictya are reassessed; the possibility of resurrecting the genus Oleorthis for some species is considered, but discounted; and the diagnosis of the family is revised.