74 PALAEONTOLOGY OF NEW YORK. 



a very gentle retral curve, abruptly bending backward as tbey approacb 

 the peripheral band, crossing which they are continued of nearly or quite 

 the same strength as above. The band is simple, limited on each side by 

 a slender carination, and marked only by the curving transverse striae. 

 The revolving stria; below the periphery are often undulating, and in 

 some examples stronger than the transverse striae, while the latter are 

 usually predominant. 



This species, when preserving the surface-markings, is well characterized 

 and readily distinguished from any other form. The spire is more elevated 

 than in P. Ella, and the volutions less rounded ; the revolving striae are finer, 

 and the regular cancellation by the concentric stria? gives a textile appearance 

 to the surface. 



The substance of the shell is more delicate than in either of the preceding 

 species, except P. delicatula, and all the specimens seen are crushed or other- 

 wise distorted ; the one figured, more nearly preserves the natural propor- 

 tions. All the smaller specimens observed are flattened from above, as shown 

 on plate 28, where the spire scarcely rises above the plane of the outer volu- 

 tions. A single large specimen, figured on plate 28, is laterally compressed 

 so that the true proportions cannot be represented. The diameter of the 

 specimens in the collection examined, ranges from three-fourths of an inch to 

 about two inches. 



In form and proportions, as well as in the cancellate surface, this species 

 may be compared with P. clathrata of Munster, but differs conspicuously in the 

 absence of the elevated band at the summit of each volution. In its surface 

 markings this species has much resemblance to the figures of P. iurbiniformis, 

 Meek & Worthen, from the Coal measures of Illinois; but the New York 

 species has a less elevated spire, greater proportional width and ventricose 

 volutions. 



Formation and localities. This species occurs in fine shales of the Hamilton 

 group at Bellona, in Yates county, N. Y., and at Monteith's Point on Canan- 

 daigua lake. A single specimen, apparently a cast of this species, has been 

 found at Fultonham in Schoharie county, N. Y. 



