382 PALEONTOLOGY 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; XLVIH, FIGS. 1-5; XLIX, FIG. 1; XCVIU, FIGS. 1, 2, 5, «, 7; XCIX, FIGS. 1-8. 



Phragmoceras spbiosum, Conbad. Third Ann. Rep. Geolog. Surv. N. Y. : Pal. Dept., p. 206. 1840. 

 Cfyrooeras (Cyrtoceras f) spinosum (Coxa.), Hall. Descriptions of New Species of Foesiif, etc., p. 41. 1861. 

 " " " " Fifteenth Rep. N. Y. Slate Cab. Nat. Hist., p. 69. L863. 



" •• " " " Illustrations of Devonian Fossils: Cephalopoda, pi. 46. 



fig. 8; pL 50, tigs. 1-4; pi. 51, tig. 1; and pi. 52, 

 tig. 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 

 striae and furrows on the internal mould of the air-chambers. Aperture 

 slightly contracted. 



