418 /'l LMOSTOLOQ Y OF NEW YORK. 



This species may be distinguished from N. bucinum by its smaller size, more 

 closely coiled volutions, and more regular surface-markings, especially in the 

 i-ven and closely arranged revolving striae. It differs from N. cornulum in its 

 more elliptical transverse section, larger apical angle, and by its surface char- 

 ■rs. This is the smallest form observed among the species of this genus 

 in the Hamilton group, and it is of rare occurrence in the collections. 



Formation and localities. In the coarser, arenaceous shales of the Hamilton 

 group, near Cazenovia, Madison county, N. Y. 



Nautilus maximus. 



PLATES LXIII, LXIV, AND SUPPLEMENT. 



Cyrtoceras maximum, Conrad. Qeolog. Stirv. of N. Y. : Piil. Dept., First Ann. Rep., p. 117. 1838. 

 Nautilus maximus (Conb.), Hall. Illustrations of Devonian Fossils : Cephalopoda, pi. 64, fig. 1 ; pi. 64 A, 



fig. 1. 1876. 



Shell very large, subdiscoid, gibbous, becoming very ventricose. Volutions 

 about three, contiguous, not re-entrant. Umbilicus wide and deep, exposing 

 all the volutions. Transverse section subcircular, flattened on the concave 

 dorsal side. Tube regularly and gradually enlarging to a point near .the 

 aperture. Apical angle about 14°. 



Chamber of habitation very large and ventricose, occupying half a volution 

 or more. In the larger individuals it is free from the inner volution for 

 about one-third of its length. Length of the grand chamber more than 

 twice its greatest diameter, gradually contracting toward the aperture from 

 a point about two-thirds pf its entire length from the base. Aperture 

 slightly oblique to the axis of the tube, opening upward. Air-chambers 

 numerous, regular and very deep, gradually increasing from the apex, and 

 measuring on the convex side, sometimes more than thirty mm. ; the last 

 one shallower than several of those preceding. 



Septa regular, distant, very concave, the concavity greater than the depth 

 of the air-chambers ; strongly imbricating. The distance between the septa 

 is variable in different specimens, but in the same individual is nearly con- 

 stant, with a gradually increasing distance. Measurements taken from the 

 convex side of the outer Volution of three individuals show four chambers in 



