470 I'ALMOSTOLOGY OF NEW YORK. 



GONIATITES OwF.M. 



PLATES i. win, MGS. I B; i.xxiv, fig 9. 



CimMttn Oioenl, Hall. TUfrteentil Rep. N. Y. State Cab. Nat. Hist., pi. 100, figs. 11, 12. 1800. 

 •• •• Illustrations 06 Devonian' FoaaUa s Cephalopoda, pi. 78, figs. 8-8. isTii. 



Shell discoid, depressed suborbicular, with the lateral faces somewhat flattened, 

 and the periphery regularly rounded ; the greatest lateral diameter equal to 

 about twice and a half the thickness of the disc. 



Volutions ventricose, about six to eight or nine, the lateral and ver- 

 tical, or dorso- ventral, diameters being nearly equal. All the turns are 

 exposed in the umbilicus to about one-fourth or less of their width, the 

 remaining tbree-fourths or more being embraced in each succeeding volu- 

 tion. Umbilicus deep and of moderate width, subject to considerable 

 variation; the margins descend by a series of vertical steps, the inner face 

 of the volutions being flat and essentially rectangular to the lateral face. 

 Transverse section semi-elliptical, the height equal to the diameter at the 

 base, which is deeply impressed by the preceding volution, leaving the por- 

 • tion beyond its periphery nearly equal to, or a little more than the embrac- 

 ing portion of the volution. The rate of enlargement of the volutions, in a 

 well-preserved specimen of medium size, is from thirteen mm., the diameter 

 of the inner of two volutions, to twenty-one mm., the diameter of the 

 outer one, and in a larger individual the proportions are about as twenty- 

 one to twenty-eight mm. In a smaller specimen, having its largest diameter 

 of twenty mm., the rate of increase is from six to nine mm. in a single 

 volution. 



Chamber of habitation not satisfactorily determined. In many specimens 

 it appears to occupy more than an entire volution, there being no external 

 indication of septa, as in figures 7 and 8 of plate 73 ; while in other forms, 

 of similar dimensions, there are evidences of septa in the exterior volu- 

 tion. A specimen, having a lateral diameter of ninety mm., and cut in 

 horizontal section, shows a full volution and a half, free from air-chambers. 

 In one specimen, where the basal portion of the outer chamber is clearly 



