with fossils of marine origin, in no wise indicates that the merostomes were marine. The Siluric fauna of Bohemia is one of the best illustrations of this class, and I shall consider it in detail.
Barrande's work on the faunas of the Palæozoic rocks of Bohemia has conclusively shown that the trilobites and other crustacea, as well as the eurypterids reached their acme in numbers in the Siluric, constituting the third fauna E. The upper part of this showed a far more prolific development of life than did the lower, as is readily brought out by the following figures. In the Lower Siluric (E e1) Barrande records sixteen species of trilobites and ten species of other arthropods among which he includes phyllopods, ostracods, eurypterids and cirripedes; for the Upper Siluric (E e2) the corresponding figures are 82 and 24, making a total of crustacea (and eurypterids) for the Lower Siluric of 26, for the Upper 106. Furthermore, the crustacea, though represented by so many species were not the dominant forms of life, for the Siluric, especially the upper part, marked the period of greatest development of the cephalopods which were represented by 665 species. As I stated in an earlier part of the paper, Barrande does not give horizons of smaller taxonomic value than his "bands" which correspond to the first subdivision of the periods, and it is therefore impossible even to approach the niceties of correlation which can be attained in America; one cannot determine the precise level even within several hundred feet for any particular occurrence. However, there is no reason to doubt that all of the Siluric of Bohemia was marine. Considering the nature of the fauna of that period and the number of species which Barrande was able to describe even so early as 1852, his explanation for the fragmentary character of the eurypterids, as due to their having been the food of the cephalopods, seems inadequate. If the trilobites were able to live in the same sea with cephalopods and escape unscathed, so that their remains were preserved in wonderful perfection, why should the eurypterids have been so voraciously attacked? It is doubtful if the eurypterids were of so different an internal nature from the trilobites that they should have been more palatable, nor were their exoskeletons more fragile. In the Siluric sea 814 species of cephalopods are known to have existed, as compared to 97 species of trilobites. Thus there were eight or nine species of Cephalopods to each species of trilobite, while the number of the individuals of the former vastly exceeded that of the latter. Surely in the great struggle for existence which was taking place, the cephalopods, if they fed
