430 I'.l LJBONTOLOQT OF NEW YORK. 



the transverse diameters at the periphery and umbilical margins is distinctive, 

 while the presence of a row of nodes upon the umbilical margin in that species 

 constitutes a marked difference between the two forms. 



This and the two preceding species form a natural group, very distinct from 

 the other Devonian forms of the genus Nautilus. Their discoidal form, angu- 

 lar transverse section, position of the siphuncle, and character of surface orna- 

 mentation, indicate their relation to many of the Carboniferous forms of the 

 genus. Although they may be true Nautili, in the ordinary acceptation of the 

 terra, they possess features which give them a Goniatitic aspect. The course 

 of the septa in the last-described form is almost precisely the same as in 

 Goniatites Vanuxemi, with the simple difference that, the siphuncle being so far 

 beneath the ventral surface, the septa are not extended along its walls to 

 form the narrow ventral lobe which penetrates the preceding air-chamber. 

 I have, therefore, intentionally used the same terms in describing these parts. 



In every aspect of form, position of siphuncle, curvature of septa and surface 

 ornamentation, the three forms last described are remarkably distinct from all 

 the other Nautili described in the present volume. 



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

 Schoharie ; at Manlius and other places in Central New York, and is nowhere 

 known above the horizon of that formation. 



Notb. — Mr. Vanvxkm, in his report above cited, remarks, p. J47, concerning the Marcellus Qoniatite: 

 "This species in mure abundant, and some are of great size. A fragment of one was found, which, when 

 perfect, must have been nearly a foot in diameter." It is evident, therefore, that he regarded the Large form 

 as O. ilarcelUnxlt, and recognized the smaller ones as Q. expansus. The Nautilus Marcellensis {OofdaUtt* 

 of Vam'zkm) is not known to reach a larger size than those figured on plate 65; and it is far less abundant 

 than G. Vanuxemi. The fragment of large size, referred to above, is a part of the outer chamber of Q. Van- 

 uxemi; and the original specimen of the Marcellus Goniatite, illustrated on plate 109, was imbedded in a 

 separated fragment of the grand chamber of another specimen of Ct. Vanuxemi. From the remarks above 

 cited, and without sufficient knowledge of the typical specimen, I hail concluded that the two species of 

 Vaxcxbm had been founded on the different phases of O. Vanuxemi, and proposed the name Discites ornatut 

 for the nautiloid form. 



