386 
PALAEONTOLOGY OF NEW YORE. 
Air-chambers regular, numerous, gradually increasing in depth toward the 
grand chamber, varying from three to seven mm. in the length of twenty- 
eight air-chambers. Septa smooth, moderately concave, with an areola 
around the insertion of thb siphuncle. Sutures straight and at right angles 
to the spiral axis. 
Siphuncle near the ventral side, moniliform; not satisfactorily observed. 
Test and surface-markings unknown. Internal mould essentially smooth, 
with the sutures moderately impressed. 
The specimen figured on ph. 100 has a diameter, measured from the aper¬ 
ture across the disc, of 180 mm., and the greatest diameter of the tube is 
fifty-two mm. 
This species is distinguished from G. spinosum by the absence of revolving 
rows of spines or nodes, and a more gradually enlarging tube. It differs from 
G. Eryx in its smaller volutions and more openly coiled spiral. 
Formation and localities. In the Schoharie grit, Schoharie and Albany 
counties, N. Y. 
Gyroceras Eryx. 
PLATES LVIII, FIG. 1 ; CIII, FIG. S. 
G-yroceras Eryx, Hall. Descriptions of New Species of Fossils, etc., p. 39. 1861. 
“ “ “ Fifteenth Rep. N. Y r . State Cab. Nat. Hist., p. 67. 1862. 
“ “ “ Illustrations of Devonian Fossils : Cephalopoda, pi. 48, tig. 1. 1876. 
o 
Shell large, discoid, coiled, making about two nearly contiguous volutions. 
Transverse section broadly oval; ventro-dorsal diameter the longer. Tube 
regularly enlarging from the apex to the aperture. Apical angle about 10°. 
Chamber of habitation large. Aperture not observed. 
Air-chambers numerous, regular, having, on the outer volution, a depth of 
fifteen min., measured on the convexo-ventral side, and of six mm. on the 
concavo-dorsal side. Sutures straight and at right angles to the spiral axis 
of the tube. 
Siphuncle ventral, near the chamber walls, nummuloid, expanding to a 
diameter equal to the depth of the air-chambers. 
