438 PALJBOSTOLOGY OF -\7.ir YORK. 



to twelve in the chambered portion, and about as twelve to fifteen at the 

 aperture. Many specimens, in their greatest extent, have a diameter of 150 

 to 200 nun.; one specimen haa a diameter of over 300 mm., with the 

 periphery of the chambered portion measuring about the same, and the 

 periphery of its incomplete grand chamber 500 mm. A specimen, measur- 

 ing over 200 mm. in its lateral diameter, has a transverse diameter at the 

 aperture of 80 mm.; the lateral diameter of the same specimen at the last 

 air-chamber being about seventy-three mm.; with the thickness of the 

 shell added, the diameter would be about 75-77 mm. at this point. 



This species is very closely allied to G. Bohemicus, Barrande, and presents 

 even a greater variety in the modifications of its form and surface characters. 

 It attains a larger size than the Bohemian species, and the last volution is more 

 rapidly expanding. 



With a single exception this is the earliest appearance of the Goniatitic type 

 in our strata, and its modifications of exterior form and its great expansion in 

 size are truly remarkable. Its associations and the surrounding physical con- 

 ditions mark an epoch of sudden change in the geological history, of which we 

 have no parallel in the preceding record, andscarcely one of equal magnitude 

 or degree in the entire palaeozoic series. Its parallel in physical conditions 

 and the aspect of the fauna are only to be found in the deposits of the carbon- 

 iferous seas. 



Formation and localities. In the Goniatite limestone of the Marcellus shale, 

 at Schoharie, Cherry Valley, and near Manlius and Marcellus, in Onondaga 

 county, N. Y. 



GONIATITES UNILOBATUS. 



PLATES LXXI, FIGS. 15, 16; LXXIV, FIG. 5. 



Qonlatita unilobatut, HlIX. Descriptions of New Species of (ioniatidic, p. 1. May, 1874. 



" Twuity-wventh Hop. N. Y. State Mug. Nat. Hist., p. 133. 1875. 

 " " Illustrations of Devonian Fossils: Cephalopoda, pi. 71. 1876. 



Compare QonUUite* Vanuxcmi, in tlie preceding descriptions and following illustrations. 



Suell discoid, the sides flattened, and joining the periphery at an obtuse angle. 

 Periphery somewhat flattened; the proportions of the thickness- and diameter 

 of the disc not ascertained. 



