Page:The Habitat of the Eurypterida.djvu/64

 occupied land waters chiefly. In the Devonian and Carboniferous periods, in which the eurypterids reached their climax and passed into their decline, and where they seem to have been in their more natural relations, they are associated with land plants, scorpions, insects, fishes, and fresh-water amphibians, which seem to imply a fresh-water habitat. In the light of these facts, the more common inference has been that they were originally marine forms, and became adapted later to brackish and fresh-water conditions. The alternative inference is that they were originally denizens of the land waters, and that their remains were occasionally and sometimes quite freely carried out to sea by stream waters, and were thus fossilized with marine forms. Their occasional presence in the earlier periods is thus explained, while their seemingly sudden appearance in abundance and in gigantic forms in the closing Silurian, and their prominence in the land-water deposits of the Devonian and Carboniferous finds ready explanation in the fact that these are the first well-preserved fossil-bearing deposits of land waters. In these deposits the eurypterids often appear without any marine associates, while occasionally there are some marine or at least brackish water forms associated with them, implying either that they lived in brackish or salt water at times, or that their remains were carried out into such waters by the land streams or estuarine currents" (33, 412).

It is to be noted that European authors have said very little about the habitat of the eurypterids, though there are a few brief references. Geikie is the one exception, for he has a good deal to say about the merostomes and the faunas which occur with them. I shall at this point merely quote a few of these passages, written in the discussion of the Upper Siluric occurrences and of those in the Old Red sandstone. "Vegetable remains, some of which seem to be fucoids, but most of which are probably terrestrial and lycopodiaceous, abound in the Downton sandstone and passage-beds into the Old Red Sandstone. The eurypterid genera continue to occur, together with phyllocarids (Ceratiocaris) and vast numbers of the ostracod Beyrichia (B. Kloedeni). Prevalent shells are Lingula cornea and Platyschisma helicites. The Ludlow fishes are also met with" (74, 961). In the discussion of the deposition of the Old Red Sandstone in basins Geikie says: "An interesting confirmation of the view that these basins were isolated is supplied by the occurrence of what is believed to be the oldest lacustrine or fluviatile mollusk yet known, Amnigenia (Anodonta, Archanodon) jukesii. This shell has been