upon crustaceous animals at all, would scarcely have used such nice selection so that the eurypterids alone were consumed, while the trilobites continued to flourish.
Of a certainty, some more rational explanation must be sought. This occurrence in Bohemia is one of the rare ones in the Siluric in which the eurypterids are found associated with an abundant and unquestionable marine fauna. Yet the facts, that no complete individual has been found, that even the fragments are of so uncertain a character that some which at first were supposed to belong to separate species have with more study been found to belong to the same species, and finally that the eurypterids, of all the myriad organisms which lived in that sea, should have been broken to fragments of which only a few are found—these facts will not admit of explanation on the ground that the eurypterids lived in the sea. They must have lived in some other aqueous realm besides the sea, and one is again led to the conclusion that they must have lived in the rivers. The facts of migration and the relations of the Bohemian forms to those in other parts of the world strongly support this conclusion. (See below chapter V).
CHAPTER V
The Geological and Geographical Distribution of the Eurypterids and the Conditions of Migration
SUMMARY OF FACTS OBSERVED REGARDING THE DISTRIBUTION OF THE EURYPTERIDS
The anomalies in the geographic distribution of the eurypterids constitute one of the most difficult phases of the problem of the habitat. The facts which have been summarized in the tables on pages 37-49, and which have been discussed in various parts of the paper up to this point, clearly lead to the following generalizations: (1) There are many cases in which single individuals are found separated geologically and geographically from other known eurypterids or eurypterid-faunas. (2) The same or closely related species may occur in regions widely separated, although in the same horizon, in intermediate regions, either no eurypterids at all are found or else those which do occur are not related to those in the other localities. (3) Eurypterids are seldom found in the same chronofauna throughout the world, but appear suddenly, now in one place, now in another
