this reason it is impossible from a study of the fauna, flora and sediments of that region alone to arrive at any conclusion as to the habitat of one group of the organisms whose remains are found there. If, for instance, we had no information from other sources regarding the ecology of the pelecypods, it would not be safe to infer that they were marine organisms because associated with brachiopods, nor would it, on the other hand, be fair to assume that they were terrestrial because ferns were embedded in the same strata. The same may be said for the eurypterids; nothing regarding their habitat can be inferred from their appearance in such beds as these sandstones with a commingled marine and terrestrial assemblage of organic remains. In some cases it is possible to take account of more factors, such as the relative perfection of preservation of the various groups of organisms when one, perhaps, shows evidences of transporation and consequent maceration, or again, the relative scarcity or abundance of species and individuals. In the instance of the sandstones of Condroz, I think that it is justifiable to attach importance to the sparse and fragmentary condition of the eurypterids as compared with the abundance and good condition of the other organic remains, and to conclude that probably the merostomes did not live in the region where their fragments finally came to rest.
2. The truth of the thesis of the above paragraphs being accepted, it must be acknowledged a fortiori that a single fragment or even a complete individual in a stratum in which occur no remains of typical marine organisms, intercalated in strata which do, is not the slightest proof that the eurypterid was an inhabitant of the sea.
I may here, as an illustration, give an account of the occurrence of Strabops thacheri, the only known eurypterid from the Upper Cambric or Lower Ordovicic Potosi Limestone of Missouri. In the section near Flat River, St. François Co., Missouri, given by Nason, the Potosi formation is represented as resting disconformably upon the Bonne Terre or St. Joseph limestone of uncertain Cambric age, but probably at least Middle if not Upper Cambric. At the base of the Potosi is an edgewise conglomerate extending upward for about feet and followed by 100 feet of conglomerates and interbedded slates, the latter carrying several species of trilobites, brachiopods and an occasional Hyolithes primordialis. As was stated on p. 13, Beecher, who identified the fossils collected by Nason and who described the one eurypterid found, did not and perhaps could not state in just which layer Strabops occurred and whether it was found
