428 PALJEOXTOLOGV OF NEW YORK. 



Nautilus (Discites) Maucellensis. 



PLATW I. xv, m;*. i, I ; CIX, FIGS. 9-12, and FLATS— mti'I.i-:mi-:xt. 



Ooniatitt.1 ilarcclloigls. Yam xhm. GfeolOff. Survey of N. Y. : Rep. Third District, p. 146, fig 3. 1842. 

 Dhcitft m'wifBl. H.vf i.. Thirteenth Report N. Y. Slate Cab. Nat. His., p, 10:{, figs. 21, 22. I860.- 

 Kaulllu* (Ditcitrs) Marcelleiiti* (Yani'X.), Hall. Illustrations of Devonian Foeeils: Cephalopoda, iilate 05, 



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 rapidly, 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 middle 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 



