WATERLIME GROUP. 
889 
yet come to my knowledge. In England remains of Ceratiocaris occur as 
low as the Wenlock limestone, which may be regarded as the equivalent 
of the Niagara group. 
Notwithstanding the numerous localities and the great extension of the 
Niagara and Onondaga-salt groups through the States west of New-York 
to the Mississippi river, I have not yet seen a single representative of 
these peculiar crustaceans from any of these localities. Still the limestone 
with fish-remains in some parts of the west, as in Ohio, Michigan and 
Indiana, is far more jjrolific in these vertebrata than in any of the eastern 
localities. The same remark is essentially true of the southwestern exten¬ 
sion of these strata. Although I have examined large collections of fossils 
from the Niagara and Lower Helderberg groups from as far southwest as 
Tennessee, I have yet failed to discover any remains that could be 
identified with either of the crustacean genera Eurypterus, Pterygotus or 
Ceratiocaris. At the same time smaller collections from the upper lime¬ 
stones, or those of the age of the Upper Helderberg, have shown some 
remarkably fine specimens of the teeth of fishes. 
In Wisconsin we find strata of the same age as those containing the 
Eurypterus of New-York, and these are immediately succeeded by beds 
of the age of the fish-bearing strata of New-York. The same is true of 
Illinois, and of some parts of Iowa; but in the hitter State, I have not 
yet identified any fish-remains in the higher strata*. 
In the collections of the Canadian Geological Survey, I have observed 
some fragments bearing the peculiar surface-markings of Eurypterus and 
Pterygotus. These specimens are from Gaspe ; and from their association 
with known fossils of the age of the Lower Helderberg group, I have 
presumed them to lie at the base of that formation, and they may perhaps 
be upon a horizon varying little from that of the Waterlime group of 
New-York. 
We shall observe, therefore, that the zone of strata marking the com- 
* In 1855 I collected, among other things from the strata corresponding to the upper beds of the Onon¬ 
daga salt group at Leelaire in Iowa, a small slab covered with what appeared to be the scales of fishes. 
This specimen was sent with the others to Iowa city, and I have not since seen it. This is the only evidence 
of the occurrence of fishes west of the Mississippi river which I know. 
