The main purpose of the work is to describe all North American species of graptolites. About 700 species, varieties, and mutations are distinguished. It is further intended to establish the distribution of all forms on the continent, and thereby to elaborate the principal Ordovician and Silurian basins and their relations to the Atlantic and Pacific oceans. It is found that the pure graptolite beds with large faunas of the Deepkill and Normanskill series are restricted to the two large geosynclinal basins, the Appalachian in the east and the Cordilleran in the west. The Appalachian basin faunas have strong Atlantic (Poseidon) connections with the European, especially the British, graptolite faunas, while the Cordilleran basin faunas show unmistakable relationship to the graptolite faunas of Australia and China and thereby with the Pacific fauna. Minor differences are observed between the Normanskill faunas of the northern and southern Appalachian basin, probably indicating their respective connection with or derivation from northern Atlantic and southern Atlantic faunas. The interior lowland between the Appalachian Mountains and Rocky Mountains has afforded only scattered occurrences, mostly of sessile Dendroidea. An exception is the Southwest (Oklahoma, Arkansas, and Texas) where the Ouachita basin or geosyncline, connected with the Cordilleran geosyncline, permitted the deposition of graptolite shales.