48 Review of the New York Geological Reports. 
Fig. 3 is believed to be identical with a fossil found in slabs of 
limestone at Dudley in England, whose origin is still a matter of 
speculation. Some suppose the T'entaculites to be arms of Cri- 
noidea ; others think they may be spines of Leptena. 
A columnaria, a peculiar Strophomena, and an Agnostis, per- 
haps the pisiformis, are enumerated as occurring in this forma- 
tion. 
{t is doubtful whether any strata identical with the water lime 
group of New York, exists in the West. It is true that one of 
the uppermost beds on the Falls of the Ohio is lithologically the 
same, and contains a Tentaculites and an Avicula; but they ap-. 
pear to be of species distinct from those which have been found 
in the New York water lime ; besides, as we shall by and by see, 
the western hydraulic limestone is superimposed on beds which 
contain fossils identical with some in the upper Helderberg series, 
which proves it to occupy a higher geological position. 
Pentamerus Limestone. (Part of No. 6 of the Pennsylvania 
survey. }—This, the third member of the Helderberg series, has 
received its name from the constant occurrence of a helmet-sha- 
ped Pentamerus, fig. 1 of the following wood cut. The name 
however is very objectionable, inasmuch as it does not distinguish 
it from other Pentamerus beds both below and above it. 
This limestone, though well developed in-the southern part of 
the state all along the Helderberg range, and in some of the mid- 
dle counties, is not a universal formation. In thickness it varies 
from ten to eighty feet, and usually presents the appearance of 
an uneven bedded, rough, suberystalline and highly fossiliferous, 
blackish gray, slaty limestone, with an interlamination of shale. 
The fossils figured in Vanuxem’s report, as characteristic of the 
Pentamerus limestone, are here given, 
Vanuxem’s Report, p. 117, 
