4 7.; PALEONTOLOGY OF NEW YORK. 



This species differs from all the other forms with which we are acquainted. 

 Although bearing some general resemblance to Goniatites Oweni, it differs in 

 wry important particulars, especially in the closed umbilicus, the less rotund 

 periphery, and the simple, linguiform, mucronate, ventral lobe. The species 

 was originally identified with G. rotatorius, de Koninck, to which it bears a very 

 close resemblance. An examination of the original of de Koninck's species 

 shows a greater rotundity of the periphery of the volutions, and a depressed 

 area around the umbilicus, corresponding with the description given. These 

 features may also be observed in a comparison of the figures of the two 

 species. G. rotatorius is stated by de Koninck to have a diameter of eleven 

 centimetres, which nearly corresponds with the figure given by him. In that 

 figure nineteen air-chambers are shown; and in a specimen of G. Ixion, of 

 eighty-five mm. in diameter, twenty-two air-chambers are exposed. A speci- 

 men of G. Ixion, having its greatest diameter forty-seven mm., exposes nineteen 

 air-chambers in its entire outer volution. Noting such differences in the 

 character of the two forms, I am still disposed to continue the American form 

 under a distinct designation. 



In the general form of the shell and the direction of the septa, this species 

 may be compared with G. Mithrax, in which the lateral lobe is obtuse and 

 rounded at its extremity. 



Formation and locality. In the Goniatite limestone of Rockford, Ind. 



Goniatites Lyoni. 



PLATES LXXn, FIG. 12; I.XXIII, FIGS. 9-11; LXXIV, FIG. 7. 



Ooniatitei Lyoni, M.-W. Proc. Acad. Nat. Sci. Phila., vol. 12, p. 471. October, 1860. 

 Geolog-. Surv. Illinois, vol. 2, p. 165, pi. 14, fig. 11. 1866. 

 Hyas, Hall. Thirteenth Rep. N. Y. State Cab. Nat. Hist., p. 102, figs. 17, 18. December, 1860. 

 " Lyoni, M.-W. Hall: Illustrations of Devonian Fossils: Cephalopoda, pi. 72, fig, 12; pi. 73, 



fi(fs. 9-11. 1876. 



Shell discoid, depressed, often flattened from compression ; the thickness of 

 the disc is from eight to ten mm. where the lateral diameter is from sixty to 

 eighty mm. 



