CEPHALOPODA. 385 



The sinus is deep, and occupies a broad, flattened, revolving band, extending 

 along the ventrura. 



The internal mould of the air-chambers is marked by the obscure furrows 

 of the crenulations, and by fine, longitudinal striae. The ornamentation of 

 the ventro-lateral sides is indicated by large rounded nodes. 



One fragment, making nearly one-fourth of one volution, and embracing 

 » the chamber of habitation with thirteen attached air-chambers, has a length 

 of 180 mm., of which sixty-five mm. pertain to the grand chamber. The 

 tube of the same specimen has a transverse diameter of seventy mm. at the 

 aperture, and a dorso-ventral diameter of forty-six mm. at the same point. 

 The chamber of habitation of a small individual has a length of twenty- seven 

 mm., with diameters of nineteen and twenty-eight mm. at the aperture. 



This species is distinguished from any of the other forms described in this 

 volume by its transverse section, very gradually enlarging tube, the ornamen- 

 tation of the test, and the character of the internal mould. 



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

 near Manlius, N. Y. 



Gyroceras validum. 



PLATES ILIX. FIG. 2 ; C, FIG. 1. 

 Oyrocerai validum, Hall. Illustrations of Devonian Fossils: Cephalopoda, pi. 51, fig. 2. 1876. 



Shell large, subdiscoidal, coiled in a free spiral, and making more than one 

 volution and a half. The distance between the chamber of habitation and 

 the adjacent inner volution is nearly twice the diameter of the inner volu- 

 tion. Transverse section subcircular. Tube regularly and gradually enlarg- 

 ing from the apex. Apical angle about 8°. 



Chamber of habitation large ; its greatest diameter is at a point about 

 two-thirds of the length from the last septum, directed outward, tangent to 

 the spiral axis of the tube. The sides slope gradually from near the middle 

 of the chamber to the aperture, which is slightly expanded. 

 49 



