CEPHALOPODA. 
447 
Goniatites orbicella. 
Goniatites orbicella, Hall. Thirteenth Rep. N. Y. State Cab. Nat. Hist., ji. 99, fig - . 8. 18G0. 
Shell small, depressed, orbicular. Volutions not exposed; number unknown. 
Umbilicus closed, and the inner volutions all embraced within the outer one, 
which is ventricose. Transverse section and rate of increase in size of the 
volutions not determined. 
Chamber of habitation incomplete, the portion remaining occupying about 
one-quarter of a volution. Aperture not determined. Air-chambers numer¬ 
ous, regular, very shallow at their origin and gradually increasing in depth 
till near the periphery, where they are about .75 mm. in depth, the outer 
one being slightly deeper than the preceding one. 
Septa thin, curving gently forward from their origin, and making a slight 
retral curve about the middle of the lateral face of the volutions, and 
advancing with an increasing curvature, are again recurved from a point 
about one third the width of the volution from the periphery, thence passing 
to the ventral margin. This curvature gives a low, undefined saddle on the 
inner half of the volution, a shallow lobe in the middle, and a broader and 
more elevated saddle on the outer half of the volution. Periphery unknown. 
Suture lines distinctly marked upon the surface, and the septal margins 
slightly imbricating. Siphuncle unknown. 
Test not observed. Surface-makings undetermined. 
The cast of the interior preserves some evidence of lamellose striae, and 
upon what appears to be the inner, nacreous layer are evidences of fine undu¬ 
lating striae, quite different from those pertaining to the exterior surface. 
The only specimen observed has a lateral diameter of nine mm.; but its 
comparative thickness cannot be determined. 
This species is smaller than any other known in the rocks of New York. It 
differs from any other species in the direction of the septa and the position of 
the outer saddle. 
Formation and locality. The single known specimen is from the Hamilton 
shales, at Ludlowville, Cayuga county, N. Y. 
