382 
PALAEONTOLOGY OF NEW YORK. 
ridges are bent suddenly backward, forming semi-tubular spines or retral 
arches, having an elevation of about fifteen mm. Sinus deep, very broad, 
rounded. 
One large fragment, making nearly one-fourth of one volution, has a length 
of 250 mm., and a diameter of eighty mm. at the aperture. Another smaller 
specimen has a length of 230 mm., and shows sixty-five mm. of the chamber 
of habitation, and about twenty air-chambers. 
This species is distinguished by its large size and the character of the surface 
ornaments. From G. spinosum it differs in its smaller curvature, transverse 
section; the lines of growth not undulating between the rows of spines; and 
in the less regularity in the ornamentation of the test. „ 
Formation and localities. In the Schoharie grit at Schoharie, and in the 
Helderberg mountains; and in the limestone of the Upper Helderberg group, 
at Schoharie, N. Y. 
Gyroceras spinosum. 
PLATES XLVII, FIG. 8; XLVIII, FIGS. 1-5; XLIX, FIG. 1; XCVIII, FIGS: 1, 2, 5, fi, 7; XCIX, FIGS. 1-8. 
Phragmoceras spinosum, Conrad. Third Ann. Rep. Geolog-. Surv. N. Y. : Pal. Dept., p. 206. 1840. 
Gyroceras ( Cyrtoceras?) spinosum (Conr.), Hall. Descriptions of New Species of Fossils, etc., p. 41. 1861. 
“ “ “ “ “ Fifteenth Rep. N. Y. Slate Cab. Nat. Hist., p. 69. 1862. 
- “ “ “ “ “ Illustrations of Devonian Fossils: Cephalopoda, pi. 46, 
fig-. 8; pi. 50, figs. 1-4; pi. 51, fig. 1; and pi. 52, 
fig. 1. 1876. 
Shell curved, making more than one volution; coiled in an open spiral. The 
distance between the outer and the adjacent inner volution is less than the 
diameter of the tube of the inner volution. Transverse section subcircular; 
lateral diameter a little the longer. Tube regularly and gradually enlarging 
from the apex to the aperture. Apical angle about 10°. 
The chamber of habitation has a length of one-third more than the diam¬ 
eter of the tube at the last septum. Crenulations showing as fine, revolving 
strife and furrows on the internal mould of the air-chambers.. Aperture 
slightly contracted. 
