Page:The Habitat of the Eurypterida.djvu/201

Rh discovered in these beds plant remains related to Psilophyton, and a fish which Traquair describes as Cephalaspis lornensis (Macconochie 157, Traquair 273).

Geikie calls our attention to what is believed to be "the oldest lacustrine or fluviatile mollusk yet known, Amnigenia (Anodonta, Archanodon) jukesii. This shell has been found in the Upper Old Red Sandstone of Ireland and England, associated with land-plants, (Archaeopteris, Sphenopteris, Bothrodendron, Ulodendron, Stigmaria, Calamites) fishes (Coccosteus) and arthropods (Eurypterus).

We have now completed the discussion of the significance of the eleven most important eurypterid faunas, the ones which it has seemed to the writer offered the most material from which to draw deductions. In addition there is a certain group of occurrences which appear to be able to throw little light upon the determination of the habitat, and they have not been discussed so far, for, if from the best material which we have at hand it can be proved that the eurypterids lived in the rivers from the very beginning of their history, then we need be no more distressed at finding a fragment among marine remains than we are when we find a single leaf or piece of wood associated with brachiopods and molluscs. But, lest the advocates of the early marine habitat of the eurypterids should complain that I pass over lightly the very cases which seem to prove conclusively to them that their view is correct, I shall take up those cases briefly and show wherein they do not prove what they are supposed to; but rather if of any weight at all, indicate that the eurypterids did not always live where their remains were entombed. These remaining instances, then, fall into three groups.

(1) The presence of a single eurypterid fragment or perhaps two or three fragments associated in the same stratum with a typical, well preserved, marine fauna.

(2) The presence of a single eurypterid fragment or complete individual in a stratum barren of other fossils, but immediately preceded and succeeded by strata carrying marine fossils.

(3) The presence of quite a number of fragments in scattered occurrence, but associated intimately with a typical marine fauna.

To the first group belong the following:


 * Echinognathus clevelandi, Utica shale, Upper Ordovicic.