33G PALEONTOLOGY OF NEW YORK. 



external form of the chambered portion, but the air-chambers are much deeper. 

 From G. Fischeri, of the Hamilton group, this species differs in its point of 

 greatest gibbosity, more rapidly contracting chamber of habitation, shallower 

 air-chambers, and transverse section. 



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

 Delhi, Delaware county, 0. 



Gompiioceras Fischeri. 



I'l.ATK XI.V, FIGS. 5, 6. 



Bompkoeera* (Apiicenu) Fiscfieri, Hall. Thirteenth Rep. N. Y. State Cab. Nat. Hist., p. 10G. lStio. 



Fixc/ieri, Hall. Illustrations of Devonian Fossils: Cephalopoda, pi. 45, figs. 5, 6. 1 876. 



Shell large, fusiform, slightly curved ; curvature exogastric. Transverse sec- 

 tion circular. Tube regularly enlarging from near the apex to the point of 

 greatest transverse section, which is posterior to the chamber of habitation, 

 at the third or fourth septum ; thence more gradually contracting to the 

 aperture. Apical angle about 30°. Apex attenuate, and more curved than 

 the remaining portion of the tube. 



Chamber of habitation large ; length a little less than the greatest trans- 

 verse diameter ; dorsal side nearly straight ; ventral side sloping regularly to 

 the aperture. The crenulated band, as shown in the cast, narrow, marked 

 by strong ridges and intermediate furrows, which are carried over the walls 

 of one or two of the last air-chambers, and may be obscurely traced over the 

 internal mould of the entire chambered portion. 



Aperture large, oval. Small aperture marked by a broad, gentle bend in 

 the margin on the ventral side. 



Air-chambers regular, gradually increasing in frequency toward the apex, 

 varying in depth from four to eight mm. in the length of ninety mm. ; the 

 last one or two, at the base of the chamber of habitation, shallower than the 

 preceding. Septa smooth and thin, so far as observed, and showing a con- 

 siderable degree of concavity. Sutures straight and horizontal. The internal 

 mould of the walls of the air-chambers is marked by a longitudinal carina 

 along the line of the siphuncle and under the sinus in the surface-stria;. 



