362 PALJEONTOLOQT OF NEW YORK. 



Cyrtoceras (Gomphoceras ?) formosum, n. sp. 



PLATE XCV, FIGS. 8, 9. 



Shell arcuate, exogastric. Point of greatest transverse section apparently near 

 the middle of the chamber of habitation. 



Chamber of habitation large, with the sides sloping very gradually to the 

 aperture. 



Aperture comparatively large ; its characters have not been fully observed 



Air-chambers, septa and siphuncle unknown. 



Tube ornamented with regular, shallow, transverse furrows, four in the 

 space of twelve mm., with minutely undulating lines of growth between the 

 ridges, crossed by regular, continuous, sharp, crenulating striae, of which 

 there are six in the space of seven mm. Near the aperture the transverse 

 furrows disappear, and the surface shows coarse, lamellose lines of growth. 

 The peculiar surface ornamentation here described gives the tube a very char- 

 acteristic, cancellated appearance. The furrows and lines of growth make a 

 decided sinus on the ventral side. 



The fragment figured, belonging to the chamber of habitation, is much 

 compressed, and has a length of nearly eighty mm. 



This species is characterized by the remarkable surface ornamentation, which 

 bears no similarity to any of the other forms described in this volume. It is 

 doubtfully referred to the genus Gompiioceras on account of its gibbous chamber 

 of habitation and the evident curvature of the tube, while the ornamentation 

 is similar to several species of Cyrtoceras from the Silurian system. 



Formation and locality. In the shales of the Hamilton group, at Dresden, near 

 Penn Yan, Yates county, N. Y. 



