28 PALAEONTOLOGY OF NEW YORE. 
Surface marked by fine subequal concentric striae, crossed by finer revolving 
striae; the former variously undulated upon the surface, indicating sinu¬ 
osities in the aperture at different stages of growth. In older shells the 
striae 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 striae are croAvded 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 turbinata 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, 6 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 specimens 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 
