Page:The Habitat of the Eurypterida.djvu/236

228. The eurypterid-bearing formations which, mainly on lithological grounds, are thought to have come from Atlantica are (1) Bertie, (2) Rondout, (3) Manlius (4) Siluric waterlimes of Oesel, (5) Waterlimes of Gotland, (6) Wenlock of Scotland, (7) Old Red sandstone. The faunas of these various formations will be taken up in detail with a view to determining the relations between individual species and between the faunas inter se.

Of the above mentioned formations and their contained faunas, the first three, which are North American, are quickly disposed of. The Rondout waterlime has thus far yielded but a single species, and this is the same as one from the Bertie, namely, Eurypterus remipes. Similarly, only one species is known from the Manlius, a number of specimens, for the most part poorly preserved, having been found in various localities ranging from Albany, Herkimer, Madison and Onondaga counties, New York, to Put-in-Bay, Lake Erie, where it occurs in the stratigraphically older early Monroe beds. Only one specimen has been found in which the abdomen is preserved, the remaining occurrences being only of carapaces, and even these are often poorly preserved. In outline of carapace and lack of ornamentation thereon, this species more closely resembles E. brewsteri from the Arbroath paving stones than any form known from North America, though the similarity to E. lacustris from the Bertie is not to be overlooked. Thus, the only known eurypterid from the Rondout is the same as a species from the Bertie, and the single species from the Manlius and the lower Monroe shows affinities to one from the Bertie and to one from the Old Red sandstone. With these two so easily dismissed, we may turn to a detailed discussion of the Bertie fauna in which connection it will be necessasy to establish the complete affinities of each species by a detailed morphological and phylogenetic comparison with species in preceding and contemporaneous faunules in America and Europe; the centres of dispersion and the routes of migration must be carefully studied, and the possibilities of fluviatile and marine distribution must be weighed. More deductions can be drawn from the study of the Upper Siluric faunas than from that of any other, because of the abundant data available, the appearance of chronofaunas in widely separated localities and the relative abundance of individuals and species in several of the faunules. Because it is impossible to draw correct deductions regarding the mode of distribution of organisms in any one period from the observation of the distribution visible at that time (see p. 208 above), and since the truth is to be arrived at