Introduction 2 It is now nearly thirty-eight years since the writer found his first fossil at Cincinnati, Ohio, during the past twenty-four years of which he has devoted his entire time to invertebrate paleontology and Paleozoic stratigraphy. His professional service in these sciences had its initiative in association with E. O. Ulrich, and was continued with James Hall, C. E. Beecher, and Charles D. Walcott. Subsequently nearly all the larger American collections of Paleozoic fossils, as well as many European ones, have been examined or studied by him. For eleven years he had charge of the unrivaled collections assembled through the various government surveys, which are now deposited, together with much other material, in the United States National Museum. It was during these years of paleontologic abundance, grand library facilities, and the enthusiasm engendered through daily association with eleven paleontologists that he began the investigation of the problem of interprovincial . . .