Published online by Cambridge University Press: 14 July 2015
The hyolith orders Camerothecida Syssoiev and Diplothecida Syssoiev are here incorporated into the order Hyolithida Matthew. Morphologic features used to distinguish Camerothecida and Diplothecida are interpretive reconstructions of features presumed to have been present but not actually preserved on any existing specimens. The few morphologic features retained by those fossils are consistent with assignment to the Hyolithida. Poor preservation of the types of Hyolithes (Camerotheca) gracilis Matthew and Diplotheca hyattiana Matthew, which formed the basis for those two orders, as well as those of Hyolithes (Camerotheca) micmac Matthew in Walcott, Hyolithes acadica Hartt in Walcott, and Hyolithes matthewi Sinclair, renders generic assignment of these species uncertain. Hyolithes matthewi Sinclair is assigned to Tulenicornus Val'kov with question, and Hyolithes danianum Matthew in Walcott is here transferred to Nitoricornus Syssoiev.