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, FIG. i. 



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. Siphuncle 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. 



