The Trinucleidae: With Special Reference to North American Genera and Species

The thirteen genera, three of which are new, of the Family Trinucleidae are diagnosed or discussed, and grouped into four new subfamilies. Data relating to the stratigraphical position and range of position of each genus in Europe and North America is given. Genera belonging to three, and perhaps the four, subfamilies are known from the Ordovician of Europe and North America, but only two, perhaps three, genera are common to the rocks of the two countries. One new genus and four new species from Oklahoma, and a new variety from New York, are described. Two previously described species. Trinucleus acervulosus and Tretaspis elevata, are made the types of new genera, and Cryptolithus tesselatus, C. bellulus, and T. reticulatus are redescribed. Notes on two species from South Manchukuo are added. Some developmental stages of four species are described.