A revision of Early to Mid Ordovician Hyoliths from Sweden

Hyolith assemblages of early to mid Ordovician age in Sweden include the hyolithids Hyolithus bisulcatus Holm, H. concinnus Holm and H. innotatus Holm, which are confirmed as representatives of Hyolithes Eichwald. Dorsolinevitus Syssoiev is known from D. dispar (Holm), D. textilis (Holm) and D. vomer (Holm), and Carinolithes Syssoiev is represented by C. hospes (Holm) and C. triumvir (Holm). Sulcavitus caelatus (Holm), the type species that forms the basis for a family and even an order according to some, is redescribed; the order is suppressed. Hyolithus cymbium Holm is transferred to Stelterella gen. nov., and Theca crispata (Boll) is now the type species of Crispatella gen. nov. The unusual orthothecid Quadrotheca quadrangularis (Holm) is redescribed; the concept of Trapezotheca aemula (Holm) is emended, and Semielliptotheca dens (Holm) is transferred to Trapezotheca. Semielliptotheca Syssoiev is poorly known from only one species, S. rosmara (Holm), and that genus is now considered to be unrecognizable. Hyolithus exaratus Hadding is identified as closely related to the gastropod Lytospira norvegica Koken, and specimens of Hyolithus sp. nos 11, 12 and 13 Holm and Hyolithus sp. indet. Wiman, remain to be located.