CEPHALOPODA. 
403 
departure from a symmetrical curve, shallower air-chambers, and transverse 
section. It somewhat resembles T. Barrandei, but that species is more gibbous, 
more incurved at the apex, with a larger apical angle and deeper air-chambers. 
Formation and locality. In the Schoharie grit, at Schoharie, N. Y. 
Trochoceras? (Gonioceras?) pandum, n. sp. 
PLATE CXI, PIG. 4. 
Among the extensive collections from the Schoharie grit have been observed 
several specimens of extremely doubtful relations. The shell was originally 
nearly straight, angularly elliptical in its transverse section, and rapidly 
enlarging from the apex. 
Air-chambers numerous and very shallow toward the apex, suddenly 
increasing in depth toward the larger portion of the tube, and showing other 
irregularities. Near the apex of one specimen there are ten air-chambers, 
having a uniform depth of two mm. each. The four succeeding chambers 
measure five, seven, nine and fourteen mm. respectively. 
The sutures make a broad retral curve over each face of the tube, and are 
extended forward, convex to the aperture, over the angles. Siphunele and 
surface-markings unknown. Internal mould essentially smooth. 
One fragment with a length of fifty-five mm. Shows fourteen air-chambers. 
Another specimen, having about the same dimensions, preserves the same 
number of air-chambers, but exhibits a greater variation in their depth. 
The curvature of the sutures and the acutely elliptical transverse section give 
this form much the aspect of Gonioceras ; but the species of this genus have not 
shown such variations in the depth of the air-chambers, and none are known 
above the Lower Silurian. The absence of all distinctive characters beyond 
general form would probably assimilate it with Orthoceras ; but it is unlike 
anything yet known in that genus. It bears some relation to Trochoceras, 
and might be%associated with T. expansum or T. obliquatum , from its resemblance 
to a lateral view of a portion of one volution in these species ; but the flat sides 
of the tube, its sharply angular transverse section, and the extreme variation 
in the depth of the air-chambers are distinguishing features. 
