12 6 PALEONTOLOGY OF NEW YORK. 



a conspicuous difference between the two. In the casts, faint impressions 

 of the revolving stria) are usually preserved. 



The specimen figs. 20-22 is a cast of the interior, of remarkably rounded 

 form, and showing a slight sinus on the left beneath the apex. The dorsum 

 in fig. 22 is improperly represented as evenly convex, while there is a slight 

 angularity visible in the specimen. 



Formation and localities. In the coarse shales of the Hamilton group at 

 Hamilton, and at Pratt's Falls in Madison county, N. Y. 



PORCELLIA, Leveille. 



PORCELLIA HERTZERI. 



PLATE XVI, FIG. 24. 

 Porcellia Hertzeri, Hall. Illustrations of Devonian Fossils : Gasteropoda, pi. 16. 1876. 



Shell discoid. Volutions about four, very gradually enlarging, the last one 

 rounded on the back, becoming ventricose towards the somewhat obovate 

 aperture ; dorso-lateral margin subangular, nodose, and sloping thence to 

 the ventral margin ; ' umbilical depression broad and shallow ; the dorsal 

 margin preserving evidence of a deep sinus. 



The finer surface-markings are unknown. The dorso-lateral margin is 

 marked by distinct elongate nodes, and the sloping ventral sides preserve some 

 remains of similar markings. 



The only specimen of the species known to me has a length of about one 

 inch and a quarter, with a width of one inch. It resembles in form the 

 European P. puzo, but the elongate nodes of the dorso-lateral margin present a 

 very characteristic distinction. 



Formation and locality. In limestone of the Upper Helderberg group in Dela- 

 ware, Ohio. The species has been communicated by Rev. Mr. Hertzer, 

 of Louisville, Ky., formerly of Columbus, Ohio. 



