414 
PALEONTOLOGY OF NEW YORE. 
There is likewise sometimes, a distinct longitudinal carina, marking the sur¬ 
face of the filling of the air-chambers along the centre, on the convex ventral 
side; and the same feature is shown in the inner laminae of the shell. In 
the same position the cast sometimes preserves a gentle sinus on the ventral 
side of the chamber of habitation. 
This species, in the larger individuals, has a diameter of about ninety 
mm., with a transverse diameter of the tube, near the aperture, of sixty- 
five mm. 
This form is distinguished from N. liratus by the absence of the strong, 
revolving plications, the greater curvature of its volutions and the position of 
the siplmncle. From N. cornulum it differs in the proportionally greater trans¬ 
verse diameter, and the simple contiguity of the volutions. It has a wide 
vertical and horizontal distribution in the shales of the Hamilton group, 
occurring also in the Goniatite limestone. It becomes more common in the 
coarse, arenaceous shales of the lower part of the group in Schoharie, Otsego 
and Madison counties, especially near Cazenovia. It occurs in the higher, 
semi-calcareous shales of the groujD in the central and western part of the State. 
It also occurs near Cumberland, Md., and the adjacent part of Virginia. 
Formations and localities. In the Goniatite limestone, near Manlius; in the 
Hamilton group, at Schoharie; Cazenovia; on the shores of Cayuga and Can¬ 
andaigua lakes; near Geneseo, Avon and York, in Livingston county, and 
other localities in Central and Western New York; and at Cumberland, Md. 
Nautilus cornulum. 
PLATE LX, FIGS. 5, 6. 
Nautilus cornulum, Hall. Illustrations of Devonian Fossils: Cephalopoda, pi 60, figs. 5, 6. 
Shell subdiscoid, ovoid, gibbous. Volutions about two or more, slightly 
re-entrant, exposing nearly their entire width. Umbilicus profound. Trans¬ 
verse section subcircular, with a distinct sinus on the concave dorsal side, 
where it embraces the adjacent volution. Tube regularly and rapidly 
enlarging. Apical angle about 1G°. 
