ORTHIDES OP THE PORTAGE AND CHEMUNG GROUPS. 57 



ORTHIDES OF THE PORTAGE AND CHEMUNG GROUPS. 



In the Report on the Fourth Geological District of New- York, I de- 

 scribed one species of Orthis from the Portage group, and two species 

 from the Chemung group, and identified a third with a European species. 

 The specimen from the Portage group consists of a partial cast, which is 

 finely striated, resembling the surface-characters of Okthis ; but a farther 

 examination proves it to belong to a distinct genus : and the Portage 

 group, therefore, has not thus far furnished to the collections any species 

 of Orthis. 



In the Chemung group, within the limits of tjiis State, we know several 

 species of this genus, which occur more commonly in beds of the lower 

 and central parts of the formation. In the higher beds of this group, we 

 have at this time few evidences of the occurrence of Orthis ; while several 

 species of Productus and Spirifer are seen in the central and higher beds 

 more frequently than in the lower part of the group. 



In their geographical distribution, the larger and more conspicuous 

 species appear to be comparatively limited, since I have not found them 

 in the eastern prolongation of the group in Delaware county ; nor 

 have they been often found in Chautauque county. One or more of the 

 species are common in many localities in Tioga, Chemung, Steuben 

 and Allegany counties, and less frequent to the westward ; while some 

 smaller forms are not uncommon in the neighborhood of Leon> Randolph 

 and Conewango in Cattaraugus county. So far as investigations have 

 progressed, it has not been found practicable to identify the individual 

 beds containing these fossils to the west of Cattaraugus county ; and at 

 localities still farther west, we find a different association of fossils in 

 beds wh#!h appear to be in the same horizon. 



Note. The investigations in the Chemung group are unfinished, and we may 

 obtain farther information before the close of this volume. In the mean time, the 

 necessity of printing obliges me to send the descriptions of these species to the 

 press. 



[ Fausontolooy IV.] 8 • 



