24 PALEONTOLOGY OF NEW YORK. 



Platyostom \ i.inkata var. SINUOSA. 



PLATE XI, FIGS. 4-8. 

 Piatyottoma linrata 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 spire 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 throughout 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, FIU. 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. 



Tliis 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. 



