428 
VALffiOOTOLOGY OF NEW YORE. 
Nautilus (Discites) Marcellensis. 
PLATES LXV, FIGS. 1, 2; CIX, FIGS. 9-12, and PLATE —SUPPLEMENT. 
Goniatites Marcellensis, Yanuxem. Geolog. Survey of N. Y. : Rep. Third Disiric!, p. 146, fig 2. 1842. 
Discites orvatus , Hall. Thirteenth Report N. Y. State Cab. Nat. Hi?., p. 103, figs. 21, 22. 1860. 
Nautilus ( Discites ) Marcellensis (Vanux.), Hall. Illustrations of Devonian Fossils: Cephalopoda, plate G5, 
figs. 1, 2. 1876. 
Shell large, discoid; the greatest thickness of the disc scarcely equal to half 
the lateral diameter. Volutions three or four, contiguous, not embracing. 
Umbilicus wide and deep, exposing the entire lateral faces of the inner volu¬ 
tions. Transverse section quadrangular, trapezoidal, with the sides slightly 
convex, and the angles alate. Dorso-ventral diameter the longer, the base 
about one-third wider than the apex, or ventral side. These proportions 
change somewhat as the tube expands toward the aperture. The width of 
the convex ventral side increases very gradually, the angle being only from 
2° to 6°, the greater angle being on the outer volution of older shells. 
The concave dorsal side widens rapidljq making an angle of 26°, while the 
divergence of the lateral faces is about 13°. 
Chamber of habitation large, somewhat ventricose, the length nearly twice 
the ventro-dorsal diameter at the aperture, occupying fully half of one volu¬ 
tion, and having a capacity at least three times as great as all the chambered 
portion of the shell. Aperture oblique to the direction of the axis of the 
tube, opening slightly upward, with a deep, rounded sinus in the ventral 
margin, and a less conspicuous one on the midVlle of the lateral margins. 
Air-chambers numerous, somewhat regular, and gradually increasing in depth 
toward the base of the grand chamber. In a large specimen the increase in 
the depth of the chambers, in a single volution, as measured on the lateral 
• face, is from 3 or 3.5 mm. to 10 mm., or an increase of 7 mm.; there being 
a slight difference in the measurement in two individuals, where the diame¬ 
ter of the disc is about the same. 
Septa strongly imbricating, somewhat regularly increasing in distance 
from the apex to the base of the grand chamber, about four or five in the 
space of forty mm on the outer volution. The convexity in a dorso-ventral 
