Aspera, Spirifer verneuili, &c., and these the latter geologist assigns to the Devonian epoch.
The brachiopods, generally classed collectively as Spirifer mucronatus, follow at least five distinct lines of evolution in the Middle Devonian of North America, while more than twenty divergent lines have been observed by Grabau among the species of the gastropod genus Fusus in Tertiary and recent times.
Other common genera are Spirifer, Chonetes, Athyris, Rhynchonellids and Terebratulids, Discina and Crania.
The fossils include Syringopora, Zaphrentis, Productus, Spirifer, &c., and belong to the Carboniferous.
The lowest beds contain many fossils, including Phacops, Homalonotus, Leptocoelia, Spirifer, Chonetes, Orthothetes, Orthoceras, Bellerophon.