352 
PALAEONTOLOGY OF NEW YORK 
ber, varying from ten to fifteen mm. in the length of ninety-five mm. The 
walls of the cast are smooth and fiat, with the exception of an indistinct, 
longitudinal carina, marking the position of the siphuncle and the ventral 
side. Septa smooth, deeply concave. Sutures straight and horizontal, but 
little impressed on the internal mould. 
Siphuncle moniliform. Its exact position and characters have not been 
determined, owing to the compression of the apical portion. 
Internal mould essentially smooth. 
The specimen described is a large fragment of the chambered portion, , 
embracing about ten air-chambers, and has a length of 120 mm., with a lat¬ 
eral diameter at the larger extremity of eighty mm. 
This species is distinguished by its size, apical angle, and the great depth of 
the air-chambers, which features remove it from any of the species described in 
this volume. In G. eximium of the Upper Helderberg group the air-chambers 
have a corresponding depth, but the shell is much more gibbous and rapidly 
enlarging from the apex. 
Formation and locality. In the sandstones of the Waverly group, at Medina, 
Medina county, 0. 
GoMPHOCERAS (?) PLANUM, 11. Sp. 
PLATE LVII, FIG. 2. 
Shell large, straight, exogastric. Transverse section elliptical,—the diameters 
in the ration of three to four. Tube regularly and rapidly enlarging. Apical 
angle about 30°. 
Air-chambers regular, having a depth of 6 mm. Sepa smooth, with a 
slight concavity. Sutures straight and horizontal. 
Siphuncle small, near the ventral side, having a diameter of two and one- 
half mm. at the septa, where the tube has a lateral diameter of forty nun. 
A small areola around its insertion in the septa indicates the expansion of 
the tube in the cavities of the air-chambers. 
Internal mould smooth. 
