400 PALEONTOLOGY OF NEW YORK. 



Trochoceras Pandion. 



PLATKS LVIII, riGS. 7-9; CXI, FIG. 8. 

 Trochoctras Pandion, Hall (in part). Illustrationsof Devonian Fossils : Cephalopoda, pi. 48, figs. 7-9. 3876. 



Shell large, coiled in an open spiral, departing but little from a plane, making 

 somewhat more than one dextral volution. Transverse section broad, sub- 

 triangular, lateral diameter the longer. Tube nearly straight toward the 

 aperture, gradually enlarging from the apex. 



Chamber of habitation small, having a length equal to the diameter of the 

 tube at the last septum. Crenulations preserved as obscure furrows over the 

 cast of the walls of the air-chambers. Aperture contracted with a distinct 

 sinus in the ventral margin. 



Air-chambers regular, gradually increasing in depth toward the grand 

 chamber, varying from three to five mm. in the length of fifty mm., measured 

 on the upper, lateral face. Near the grand chamber they reach a depth of 

 seven mm., and the last one or more are considerably shallower. Septa 

 smooth, having a concavity equal in depth to one air-chamber. Sutures 

 oblique, inclined toward the aperture on the upper, lateral face of the tube, 

 and curving gently forward on the convexo-ventral side. 



Siphuncle moniliform, near the ventral side, often exposed in the process 

 of weathering. 



Test and surface-markings unknown. Internal mould smooth, preserving 

 obscure traces of the furrows of the crenulations. Sutures slightly impressed. 



One imperfect specimen, preserving about one volution, has a diameter, 

 measured across the volutions, of seventy mm. A fragment, making about 

 one-third of a volution, and consisting of twelve air-chambers, has a length 

 of seventy mm., and a ventro-dorsal diameter at the larger extremity of 

 thirty mm. 



This species is distinguished from T. eugenium by its more angular transverse 

 section, open spiral, and oblique septa. It more nearly resembles T. obliquatum, 

 which is characterized by its lesser curvature, shallower air-chambers, and 

 rapidly enlarging tube. 



Formation and locality. In the Schoharie grit, at Schoharie, N. Y. 



