known species of eurypterids throughout the world; B, the horizons in which the remains occur, with particular reference to the fades exhibited and to the exact stratigraphical position; C, the mode of occurrence of the remains, whether well preserved or fragmentary, whether a single fragment or a large number of individuals; and finally, D, the other fossils, if there are any, which occur associated with the eurypterids. These facts are all summarized in tables I-III on pp. 37–49 and in the list of faunal associates on pp. 84–91. The second chapter is a résume of the various opinions which have been held regarding the habitat of the Eurypterida. The next three chapters (III, IV and V) deal with the three chief lines of evidence which may be adduced to determine any fossil habitat, namely, the bionomic characters of the faunas, the lithogenesis of the formations in which the remains occur, and the type of migration and dispersal, marine or fluviatile, indicated by the relations existing between species and genera in synchronous faunas and by the phyletic relationships in successive horizons. In these three chapters general principles are first discussed and criteria are established for recognizing various types of habitats, sediments, and fossil faunas; the application of these criteria to the eurypterid problem is then given in detail. The conclusion reached by the author after the study of all available data and in the light of manifold theoretic considerations is that: the eurypterids throughout their entire phylogenetic history lived in the rivers.
Aside from the work done on the literature, a large amount of material has been studied, including hundreds of typical specimens of eurypterids, thin sections of some of the waterlimes, the collections of the rock types from the eurypterid-bearing horizons of Europe collected by Professor A. W. Grabau and now in the Palaeontological Museum of Columbia University; further, a number of the best sections in the field have been visited. When the present paper was nearly finished there appeared Clarke and Ruedemann's exhaustive Monograph on the Eurypterida of New York (39), which, with Woodward's Monograph of the British Fossil Crustacea, gives us the most illuminating and comprehensive work on the Eurypterida. Many important points in the ontogeny and phylogeny of the eurypterids are here set forth for the first time, and all of the North American species are described in great detail and figured in a volume of plates that surpass all former illustrations.
