oo PALJB0NT0L0Q7 OF NEW YORK. 



ra Hid partially exfoliated specimens, some remains of these surface 

 markings are usually visible, the revolving striae being first obliterated. This 

 species approaches in surface characters the P. turhinata of the Schoharie grit and 

 lltlderberg limestone; but the volutions are never so depressed on the upper 

 side, and the aperture never so straight above, nor so extended on the lower 

 side. It has usually a length of from one to two inches; young individuals of 

 half an inch in length are not uncommon. A well formed individual measures 

 one inch and a half long, with a vertical height of about one inch ; another 

 specimen, preserving its proportions free from compression, has a length of 

 two inches, with a vertical height from base of aperture to apex of less 

 than one inch and a half. A single extravagant specimen has a length of 

 three inches, with a width of aperture of nearly two inches ; the body- 

 volution, for a distance of two inches from the aperture, is more than 

 usually straight, and marked by crowded and unequal concentric striae, 

 without revolving striae, while the latter are preserved on the upper part of 

 the shell. A cast of a specimen in the Corniferous limestone of Western New 

 York, bearing no evidence of compression, has a length of more than three 

 inches, while the vertical diameter of the aperture does not exceed one inch 

 and a half. The specimens which I have seen from Ohio and the West, are 

 casts in limestone, which, not preserving their striae, are identified only by their 

 form and proportions. 



The original description of Platyostoma lineata is as follows : 



" Transversely subovate, with wrinkled reticulated striae ; aperture orbicular ; 

 spire depressed, or slightly elevated above the top of the body-whorl." 



Although no geological position is assigned to the species by Mr. Conrad, 

 and the figure given by him does not correspond with the prevailing form of 

 the specimens examined, I am still inclined to regard it as the common form 

 of the Hamilton group, of which I have seen several hundred individuals. 



Formations and localities. In the Upper Helderberg limestone throughout the 

 limestone range from east to west in New York, and in the Hamilton group in 

 the western part of the State. 



