PALEONTOLOGY: C. SCHUCHERT 
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plants, in the rivers of Paleozoic time. Some of the animals were the 
smaller eurypterids, in the Ordovician and Silurian the armored fishes 
(the ostracoderms), in the Silurian the additional lung-fishes and diminu- 
tive primitive sharks (the acanthodians) , and in the Devonian, large 
bivalve molluscs. However, there appear to have been still other 
arthropods present, such as the ceratiocarids, a stock of phyllocarids, 
the ancestral limulids (Synxiphosura) , and probably also the branchi- 
opod apodids. In the final analysis we must further admit that all 
were more or less directly dependent upon an abundance of plant food, 
and therefore that the early Paleozoic lands were clothed with vegeta- 
tion, none of which is as yet certainly known to paleontologists. In 
this connection, however, we must also point out that today in no fresh 
waters are invertebrates of any kind known attaining to 9 feet long 
or even half that length, although it takes living Limulus eight years 
to attain to sexual maturity. This implies that at least some of the 
Silurian and Devonian eurypterids reached a great age, and, living in 
the rivers, and maybe at times in the brackish-water bays, were the 
monarchs of their environment. On the other hand, if the smaller 
merostomes had lived in the sea, as did the trilobites, they would also 
have been fed upon by the armored cephalopods, the nautilids, and we 
may have evidence of this preying in the common association of Ortho- 
ceras with the eurypterids. Having no enemies to feed upon them 
in the rivers, and none that were more agile, more powerful, or more 
cunning until Devonian time, the eurypterids of the Silurian and early 
Devonian continued to live on for a long time and so attained to a 
far greater size than any of the fresh-water invertebrates of today, 
which are dominated by the more active and intelligent river fishes. 
With the ascendancy of the fishes beginning in the Devonian, we see 
a diminution and lack of structural change in the eurypterids and the 
trilobites, and the vanishing of both stocks in the Permian. 
The argument of faunal associates and their entombment, plus the 
nature of the deposits, used by Doctor O'Connell to prove that the 
eurypterids are fresh-water animals, will also apply to the ceratiocarids, 
the limulids, and the apodids. In the Middle Cambrian, Walcott 
has collected three genera of ancestral limulids and other merostomes 
(Limulava) in blue to black muds rich in kaoHn, which were "probably 
laid down in a small bay or lagoon in close connection with the shallow 
Middle Cambrian sea." In these deposits trilobites of the genera Agnos- 
tus, Microdiscus, Neolenus, Ptychoparia, etc., are fairly common. 
It may therefore be that the Limulava, the ancestral limulids, and 
the apodids were in this case also fresh-water animals drifted by the 
