476 
PALAEONTOLOGY 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 
very 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 LXXII, FIG. 12; LXXIII, FIGS. 9-11; LXXIV, FIG. 7. 
Goniatites Lyoni, M.-W. Proc. Acad. Nat. Sci. Phila., vol. 12, p. 471. October, I860. 
“ “ “ 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, 
figs. 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. 
