400 
PALAEONTOLOGY OF NEW YORK. 
Trochoceras Pandion. 
PLATES LVIII, FIGS. 7-9 ; CXI, FIG. 3. 
Trochoceras Pandion, Hall (in part). Illustrations of Devonian Fossils : Cephalopoda, pi. 48, figs. 7-9. 1876. 
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. 
