24 
PALEONTOLOGY OF NEW YORK. 
Platyostoma lineata var. sinuosa. 
PLATE XX, FIGS. 4-8. 
Platyostoma lineata v. sinuosa, Hall. Illustrations of Devonian Fossils: Gasteropoda, pi. 11. 1876. 
Several specimens of this species have been observed where the peristome 
at the base of the pillar lip is deeply indented by a sinus, as shown in the 
figures. One of the specimens figured has the sjnre slightly concave, the outer 
volution flattened upon the upper side, and symmetrically rounded below. The 
other specimen has more nearly the prevailing form, with moderately elevated 
spire, the volutions rounded above an orbicular aperture with deep sinus. 
This species, in its prevailing form, is very widely distributed within the 
limits of the State. Occurring in moderate numbers in the Upper Helderberg 
limestone from the Helderberg mountains, to Black Rock, it becomes abundant 
in the Hamilton group throughput the central and western part of the State. 
In the arenaceous shales of this group in Eastern New York, it is not a 
common form, but with the accession of calcareous matter in the deposit, it 
increases in numbers, and is one of the most common forms in localities along 
Seneca, Cayuga and Canandaigua lakes; at West Bloomfield in Ontario county, 
at Geneseo, Moscow and York in Livingston county, at Darien in Genesee 
county, and at Hamburgh on the shore of Lake Erie. 
Platyostoma defigurata. 
PLATE X, FIG. 24. 
Platyostoma defigurata, Hall. Illustrations of Devonian Fossils : Gasteropoda, pi. 9. 1876. 
The shell preserves five volutions which are rounded, gradually enlarging 
from the apex; the suture close. The surface is marked by fine concentric 
striae, which become crowded and fasciculate on the outer volution—the revolv¬ 
ing striae being very subordinate. 
This shell differs from characteristic examples of P. lineata only in the more 
elevated spire, and in preserving one more volution than in ordinary forms of 
that species. It occurs in the Hamilton group, at Canandaigua lake, N. Y. 
