68 PALEONTOLOGY OF NEW YORK. 



The specimen originally described as Euomphahis? rotundus still retains a 

 portion of the shell, bearing the same characters as authentic examples of 

 Pleurotomaria Lucina — preserving, however, an unusually broad and deep 

 umbilical depression. 



The species has had a wide geographical distribution, and its vertical range 

 is not less than one thousand feet from the base of the Upper Helderberg lime- 

 stone to the higher members of the Hamilton group. 



Formations and localities. In the Corniferous limestone ; Helderberg moun- 

 tains, Williamsville, Clarence Hollow, N. Y., and Falls of the Ohio river ; in 

 the Hamilton group, York, Moscow, Geneseo, Skaneateles lake, etc., N. Y. 



Pleurotomaria Hebe. 



PLATE XIX, FIGS. 2-7. 



Pleurotomaria Hebe, Hall. Fourteenth Rep. N. Y. State Cab. Nat. Hist., p. 105. 1861. 



" " " Fifteenth Rep. N. Y. State Cab. Nat. Hist., pi. 5, figs. 7 and 8. 1862. 



" " " Illustrations of Devonian Fossils: Gasteropoda, pi. 19. 1876. 



Shell subhemispheric, conical above, rounded upon the lower side ; the volu- 

 tions flattened on the upper side, and nearly in the same plane from the 

 apex to the outer edge of the last one ; the spire above the aperture 

 about equal to the height of the aperture. Volutions four or more, very 

 gradually expanding to the last one, which is moderately ventricose and 

 subangular at the limit of the periphery with the upper sloping sin-face. 

 Aperture somewhat transverse, broadly subelliptical. 



Surface marked by strong, revolving striae, and finer transverse ones, which 

 are strongly bent backwards on the carina of the outer volution ; strije 

 not so strong below the peripheral band. 



This species is smaller than either of the preceding, but is larger and more 

 rotund than the P. sulcomarginata of the Hamilton group. The specimens 

 examined are all imperfect, and the shell, where remaining, is crystalline, 

 impairing the surface characters. The rotundity of the lower side and the 

 depressed conical form above, are characteristic features of distinction. 



Formation and locality. Upper Helderberg group, Qlarence Hollow, N. Y. 



