CEPHALOPODA. 
407 
Nautilus liratus. 
PLATES LVII, FIG. 3; LX, FIGS. 8, 9. 
Gyroceras liratum , Hall. Thirteenth Rep. N. Y. Slate Cab. Nat. Hist., p. 104. 1860. 
“ “ “ Illustrations of Devonian Fossils : Cephalopoda, pi. 57, fig’s. 5, 6 ; pi. 58, figs. 1, 2 ; 
and pi. 60, figs. 8, 9. 1876. 
Shell subdiscoid-ovoid, trumpet-shaped, gibbous, becoming ventricose toward 
the. aperture. Yolutions about two, or more, barely contiguous and rapidly 
expanding. Umbilicus wide, exposing all the volutions. Transverse section 
subcircular 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 carinse, 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 
