2 g PALEONTOLOGY OF NEW YORK. 



Subtaci marked by tine subequal concentric striae, crossed by finer revolving 

 stria) ; tbe former variously undulated upon the surface, indicating sinu- 

 ontiefl in the aperture at dill'i rent stages of growth. In older shells the 

 stria) become lamellose and often crowded in fascicles. 



In well-marked specimens of the species, as originally described, the spire 

 rises little above the general plane of the volutions, as shown in figs. 12, 14, 

 15, 16 and 19. Figs. 20 and 24 show a more elevated spire. Figs. 23 and 24 

 represent an extremely old shell, much thickened, and showing very irregular 

 growth ; the stria? are crowded in strong fascicles, and curved backward on 

 the summit of the last volution, upon the periphery, and again below the 

 periphery. 



Formation and localities. In shaly limestone of the Upper Helderberg group, 

 in the town of Onondaga, Onondaga county, and more rarely in the Helderberg 

 mountains, Albany and Schoharie counties. Some varieties of the species also 

 occur in the Hamilton group, at York and at West Bloomfield, N. Y. 



Platyostoma turbinata var. cochleata. 



PLATE IX, FIGS. 1-11. 

 Platyostoma turbinaia var. cochleata, Hall. Illustrations of Devonian Fossils: Gasteropoda, pi. 10. 1876- 



Shell turbinate. Spire elevated, conical ; volutions about four or five ; periph- 

 ery of the last volution obtusely rounded or distinctly subangular, with a 

 sinus in the margin of the aperture ; the last volution sometimes becoming 

 free near the aperture, as shown in figs. 5, G and 7. Aperture obliquely 

 subovate or ovate ; peristome sinuous, often with a deep notch in 

 the upper margin, and sometimes continued in a columellar extension 

 below. 



The specimen! referred to this variety all agree in having an elevated spire, 

 with rounded volutions above the last one, which is almost invariably sub- 

 angular. Specimens represented in figs. 8, 10 and 11 are symmetrical, and 



