CEPHALOPODA. 447 



GONIATITES ORBICELLA. 

 Goniatites orUcella, Hall. Thirteenth Reji. N. Y. State Cab. Nat. Hist., p. 99, fig. 8. 1860. 



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 *nd 

 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. 



Tiie 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. 



