PALEONTOLOGY: C. SCHUCHERT 
729 
but all of the specimens are in fragments. On Oesel, however, the three 
or four species of eur3^terids are beautifully preserved in fine-grained 
gray dolomites or dolomitic limestones, with the original chitin of the 
animals still preserved; in fact, they have been etched out of the matrix 
and the tests mounted in Canada balsam. Here (at Attel) they are 
associated with an abundance of Leperditia angelina, Orthoceras tenue, 
and great stony heads, 2 feet across, of the hydroid Clathrodictyon 
(Twenhofel 1916). Surely these deposits are more of marine origin than 
of fresh waters. 
All of this evidence, however, the present writer grants, does not 
necessarily prove that the eurypterids were born of the sea and con- 
tinued to live in this environment until the close of the Silurian, for if 
this was their habitat, surely we should get good remains of them of- 
tener than we do in the many normal marine formations of the Paleo- 
zoic, and especially in the Trenton and Niagaran formations. It would 
seem that, if the eurypterids were wholly marine animals in the Ordo- 
vician and especially in the Silurian, they should be as common and 
as well preserved as, for instance, the marine trilobites. This is not 
at all the situation. On the other hand, the evidence does not exclude 
the eurypterids from having also lived, at least at times, in brackish 
waters, the embayments of deltas, a conclusion that Doctor O'Connell 
will have none of. Nevertheless, we shall have to accept her main con- 
clusion that the eurypterids were fresh-water animals, but with this 
modification, that they also appear to have lived at times in the brackish 
waters of more or less large bays and possibly in limited numbers even 
in the seas, just as some of the fresh-water fishes of the past have gone 
to sea. Whether they were born of the fresh waters or the ocean still 
remains a debatable question, though the evidence appears to favor 
strongly the former habitat. 
It is a well-known fact that ceratiocarids and especially ancestral 
limulids and apodids are either very rare or occur locally in much re- 
stricted beds, and these, like the eurypterids, appear to have been en- 
tombed in the marine deposits near shore. The sporadic occurrences 
of the eurypterids and their great rarity as good specimens in normal 
marine deposits lead Doctor O'Connell to believe that these animals 
are of fresh-water habitats and that they were floated by the Paleozoic 
rivers into the open sea-ways just as we see the land animals and 
plants of today transported into the seas and oceans. On the other 
hand, her idea of delta deposits appears to be that they are either wholly 
of the land or of the sea, and her sketch of the late Silurian Bertie and 
Herkimer deltas (page 116) bears out this too rigid conclusion. More- 
