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PALEONTOLOGY: C. SCHUCHERT 
development in the upper part of the Silurian where about 40 forms 
are known. There is very httle evolution after Devonian time. On 
page 9 of Doctor O'Connell's memoir is given in italics the summation 
of her studies: The eurypterids throughout their entire phylogenetic his- 
tory lived in the rivers. Lest the reader forget this thesis it is repeated 
on many subsequent pages. Though the book is argumentative and 
positive, and at times pleading in behalf of its theme, prying into and 
tearing apart all things eur3^terid, the style remains essentially scientific. 
It has been and still is widely held that eurypterids were marine ani- 
mals previous to the Devonian, that toward the close of the Silurian they 
became euryhaline or able to live in both salt and brackish water, and 
that after Silurian time they probably became wholly restricted to the 
fresh water of the lands. Even though they were regarded as marine 
animals, living associated with trilobites and brachiopods, it has long 
been a difficult problem to explain why their remains are so very rare 
in the normal marine faunas of the Upper Cambrian, Ordovician, and 
Silurian, and even when they do occur are almost always in fragments. 
Although Doctor O'Connell points out this condition of occurrence, 
she does not make of it the strongest point in her argument, and yet 
it is the one fact that seemingly cannot be explained away. On the 
other hand, the entire specimen of Strahops thacheri at Yale has attached 
to the slab two specimens of the brachiopod Obolus lamborni and a poor 
head of a trilobite; the entombment is in a magnesian limestone, and 
because of the marine fauna of the same formation as listed by Beecher, 
one still retains the impression that this oldest and most generalized 
eurypterid may at least have been an inhabitant of the sea if not born 
of it. In the earhest deposits of the Silurian (Shawangunk) the euryp- 
terids usually occur in fragments and in young specimens in thin and 
localized black shales, interbedded in a very thick and regularly bedded 
sandstone series, the material of a delta spreading into the epeiric sea. 
These beds are otherwise ahnost unfossiUferous, having associated 
with the eurypterids only Arthrophycus, a lobworm-like burrow that 
in the Medina formation is associated with marine fossils, showing 
that the Shawangunk is not a river flood-plain deposit but the sands 
of a delta under the influence of marine waters. On the other hand, 
in the latest Silurian formations of America, which are clearly not of 
normal marine waters, the eurypterids either have no marine associates 
or there are scattering specimens of cephalopods (Orthoceras, Trocho- 
ceras), bivalve crustaceans (Leperditia), and brachiopods (Lingula); 
in Bohemia, the middle Silurian, with a normal marine fauna of many 
species, has seven to eight forms of Pterygotus and one of Slimonia, 
