76 PALEONTOLOGY OF NEW YORK. 



in the elevation of the spire in different individuals, so that two varieties of 

 form might be indicated — one with the spire elevated and the volutions regu- 

 larly rotund, and the other with a lower spire and volutions less convex on 

 the upper side, with a subangular periphery. 



Formation and localities. This species occurs in the Goniatite limestone at 

 Marcellus, Manlius, and other localities of this limestone in Central New York. 



Pleurotomaria Itys. 

 plate xx, figs. 8-17. 



Turbo lineatus. Hall. Geology of New York. Surv. Fourth Geol. Dist., p. 198, fig. 1. 1843. 

 Pleurvtoiiutria linrata. Hall. Descriptions of New Species of Fossils, etc., p. 16. 1861. 



Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 44, pi. 5, fig. 3. 1862. 

 Not Pleurotomaria lineata, Qowrtms. Petrefacta. 

 Pleurotomaria Itys, Hall. Illustrations of Devonian Fossils : Gasteropoda, pi. 20. 1876. 



Shell turbinate ; spire ascending, higher than wide. Volutions four or five, 

 regularly and evenly convex, gradually expanding to the body-whorl, 

 which is ventricose, rounded below and concave in the middle; umbilicus 

 small or none. Aperture broadly oval, somewhat higher than wide. 



Surface marked by strong, regular, revolving striae on the upper and lower 

 sides of the volutions, crossed and cancellated by fine, concentric striae, 

 which are directed gently backward from the suture, and scarcely showing 

 any greater curve as they approach the peripheral band ; the band is of 

 moderate width, simple, and limited on the two sides by a linear carina, 

 within which the simple concentric striae make an abrupt retral curve ; 

 the concentric striae above and below the band are of similar character, 

 while the revolving striae are finer on the lower side. 



This species varies in form and proportions, both from natural causes and 

 from compression and accident, so that some specimens are proportionally 

 much more elevated than others. In the soft Ccalcareous shales of the Ham- 

 ilton group, this fossil frequently occurs in the condition of casts, the shell 

 having been removed during the process of decomposition by iron pyrites; 

 and it is often covered by an incrusting Bryozoan. In its greatest height 

 it measures nearly an inch and a balf, but the prevailing size is scarcely 



