WATERLIME GROUP. 389 



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 prolific 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 latter State, I have not 



. yet identified any fish-remains iu 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 Waterlirae 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 gait group at Leclaire in Iowa, a small slab covered with what ajipearcd to be the scales of fishes. 

 This specimen was sent with the otl.ers 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. 



