330 PALEONTOLOGY OF NEW YORK. 



example, preserving a large portion of the chamber of habitation, with a 

 length of ninety mm., and eleven air-chambers, occupying 100 mm., has a 

 diameter of 100 mm. 



This species is larger and more gibbous than any similar form here described. 

 It somewhat resembles G. mitra, but the position of the siphuncle and the con- 

 stricted aperture of that species is a very distinguishing feature. In G. cam- 

 marus the slope of the dorsal and ventral sides is characteristic. 



Formation and localities. In the limestones of the Upper Helderberg group, at 

 Black Rock, near Buffalo, N. Y. ; and at Columbus, 0. 



GOMPHOCEBAS MITRA, n. Sp. 

 PLATE — SUPPLEMENT. 



Shell large, straight, gibbous ; exogastric. Transverse section very broadly 

 oval or subcircular. Longitudinal section subfusiform. The point of greatest 

 transverse section is posterior to the chamber of habitation, at about the sixth 

 septum. Tube regularly and rapidly enlarging to the point of greatest gib- 

 bosity, and sloping irregularly, with constrictions, and slight expansions, to 

 the aperture. The regular enlargement from the apex gives to the cham- 

 bered portion of the shell a very characteristic, conical form. Apical 

 angle 50°. Apex acute. 



Chamber of habitation small ; length less than two-thirds its greatest 

 diameter at the base, or less than the length of the large aperture. The 

 tube at the base of the grand chamber, including several shallow air- 

 chambers, is slightly constricted. From this point the sides are convex, and 

 slope rapidly toward the aperture for a distance equal to about half the 

 length of the grand chamber, where the tube is again suddenly and deeply 

 constricted, and the sides slope gradually to the aperture. Crenulations not 

 observed. 



Aperture semi-oval ; width equal to twice the transverse diameter, or 

 three-fourths the greatest transverse diameter of the tube. The small aper- 

 ture is formed by a very broad, shallow bend or sinus from the large aperture. 



