Review of the New York Geological Reports. 313 



The Delthyris and Orthis, most characteristic of the group 

 under consideration, are embraced in this wood cut. 



C5- 



B *^ 



CO 



C5 



O 





s 



». 





I- 





a. 



GO 



■^ 





JO 



Oa cx 





ffi 



?ci 



Fig. 1 is " peculiarly typical of the group." Fig. 2 " ranges 

 from the ore beds of the Chnton group to the Niagara limestone," 

 and is considered identical with a Silurian species. So also is 

 fig. 5. A shell " apparently identical is associated with the Pen- 

 tamerus ohlongus in the Clinton group ;" it differs only " in the 

 number of radii, and the less convexity of the lower valve, from 

 the O. callactis of the Caradoc of England." 



Fig. 6 is very abundant in the shale of this group ; it differs 

 only in size from a Swedish specimen, and is very closely allied, 



