THE SILURIAN PERIOD , 557 



have been aquatic, but whether they were inhabitants of salt or 

 fresh water is not obvious. They are wholly extinct, and their 

 habitat can only be inferred from their associations. In England, 

 Sweden, and Russia, eurypterids are associated with marine 

 fossils, but they are also associated with the seeds of land plants 

 and with fish which, in the succeeding stage, seem to have occupied 

 land waters chiefly. In the Devonian and Carboniferous periods, 

 eurypterids 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. 

 An alternative inference is that they were originally denizens of the 

 land waters, and that their remains were sometimes carried out to 

 sea by streams, and thus fossilized with marine forms. Mollusks, 

 crinoids, corals, and similar marine forms are almost entirely 

 absent from the fauna of the Waterlime. The few brachiopods 

 found are usually pauperitic, as though they lived in uncongenial 

 conditions. The occasional presence of a few undoubted marine 

 forms does not so much indicate that the waters were habitually 

 saline, as that they were occasionally and partially so. 



It is at this time also that the earliest known scorpions appeared 

 both in America and Europe. They were allied to the eurypterids. 

 The European forms have been thought to be land species, though 

 this has been questioned. The sting and the poison glands have 

 been identified, and the significant name, Palceophonus, "ancient 

 murderer," applied in consequence (Fig. 406, c). The American 

 species have been thought to be aquatic. 



The presence of fishes emphasizes the peculiarities of this fauna. 

 Except for their occurrence at a few points in the Rocky Mountains 

 in the Ordovician, fish remains have not been found in America 

 until this stage. In Europe a few fishes appear somewhat earlier, 

 but nearly all the fish remains of the period yet found are in the very 

 highest horizons of the Silurian, or in the deposits that form the 

 transition to the Devonian, where they are associated with eurypterids 

 and land plants, as well as marine invertebrates. It would appear 

 that the fishes of the time were varied, and that they were the fore- 



