ORTHIDES OF 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 Orthis ; 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 this 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 which 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. 
[-Palaeontology IV.] 8 
