70 FIFTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



GENUS CYRTOCERAS (Goldfuss). 



CYRTOCERAS EUGENIUM ( n. s.). f ; |) I fl,d 

 Shell elongate : the first five or six inches from the aperture make 

 a curve of not more than half an inch. A specimen of medium 

 size measures along the outside of the curve a little more than 

 seven inches, and it may have been an inch longer when entire. 

 The transverse diameter is greater than the dor so-ventral diame- 

 ter; being as six to five at the smaller end, and in the same pro- 

 portion at an inch below the aperture, namely, one inch and a 

 half to one inch and a quarter. At the smaller extremity, the 

 divergence from a straight line along the body of the shell is less 

 than three inches, and the diameter indicates a curvature of not 

 more than a quarter of a circle. 



A larger specimen, w^here the straight portion of the shell has a 

 length of six inches, and the smaller extremity (where brolien off) 

 has a diameter of an inch; the dorso- ventral diameter, at the aper- 

 ture, is one inch and a quarter, and the transverse diameter is a 

 little more than one inch and five-eighths : it has the same diameter 

 at a point two inches beyond the aperture, while the intermediate 

 space is slightly enlarged. On the outside of the curve, the septa 

 are distant very nearly one-fourth the dorso-ventral diameter. The 

 siphuncle is upon the outer side of the curve, and close to the shell. 

 The surface is marjied by transverse elevated or sublamellose 

 lines of growth; and at intervals corresponding to the septa, are 

 strong lamellose ridges, the effects of which are shown upon the 

 cast in distinct concentric ridges which are bent abruptly down- 

 wards on the back of the shell : these ridges become less prominent 

 on approaching the aperture; but the bending of the striae continues 

 the same, and the margin of the aperture shows a sinuosity of a 

 quarter of an inch in depth by nearly half an inch in width. 



This is a remarkable and well-marked species, and may be known even in 

 fragments by the form and proportional distance of the arching transverse 

 ridges, which resemble those of Gyroceras matheri, but are twice as nume- 

 rous in equal space. 



Geological formation and locality. In the Schoharie grit at Schoharie, 

 and in the Helderberg mountains. 



[ September 



