CEPHALOPODA. 407 



Nautilus liratus. 



PLATES LVII, FIG. 3 ; LX, FIGS. 8, 9. 



Gyroceras liratum. Hall. Thirteenth Rep. N. Y. State Cab. Nat. Hist., p. 104. 1860. 



" " " Illustrations of Devonian Fossils : Cephalopoda, pi. 57, figs. 5, 6 ; pi. 58, figs. I, 2 ; 



and pL 60, figs. 8, 9. 1876. 



Shell subdiscoid-ovoid, trumpet-shaped, gibbous, becoming ventricose toward 

 the aperture. Volutions about two, or more, barely contiguous and rapidly 

 expanding. Umbilicus wide, exposing all the volutions. Transverse section 

 eubcircular or moderately transverse. Tube very rapidly enlarging. Apical 

 angle, as measured between the dorsal and ventral sides, about 16°. 



Chamber of habitation large and widely expanded, occupying a great part 

 of the outer volution. Aperture subcircular or somewhat transverse, without 

 any observed sinus in the margin, and opening at right angles to the 

 direction of the tube. Air-chambers somewhat regular, increasing in depth 

 from the apex, and becoming shallower near the grand chamber. 



Septa regular, strong, thickened and imbricating at their margins. 

 A fragment of the chambered portion, apparently extending nearly to the 

 base of the grand chamber, shows the distance of the septa to be from six 

 to eight or nine mm. on the convex side, while the distance between the last 

 two, as preserved, measures only five mm. The suture lines are strongly 

 impressed and distinctly imbricating. 



Siphuncle central or subcentral. 



Test one mm. thick on the side of the volution over the chambered por- 

 tion, and thinner on the ventral side. The septate portion of the tube is 

 marked by obscure annulations, which are less frequent than the septa, 

 becoming stronger and more conspicuous toward the apex, and obsolete on 

 the grand chamber. It is likewise ornamented by broad, rounded, longitu- 

 dinal, diverging ridges, which are more strongly marked upon the lateral 

 and concave portions. These carina?, or plications, which are narrow and 

 closely arranged near the apex, and diverge with the expansion of the shell, 

 become more or less obsolete toward the aperture, especially upon the convex 



