408 PAUBOSTOLOQY OF NEW YORE. 



portions. Near the apex they are distant from each other less than two mm., 

 ami diverge until they are at least ten mm. distant toward the aperture. The 

 interspaces are at first curved in the bottom, concave, becoming gradually 

 flattened, as the distance between the ridges increases. The entire surface 

 is marked with fine, thread-like, transverse strife; and sometimes, in the 

 exfoliated condition, with obscure, revolving striae, which appear to pertain 

 to the inner or nacreous layers of the shell. 



The internal cast is distinctly marked by the suture lines, and by the 

 strong revolving ridges; and obscurely marked by the transverse and revolv- 

 ing striae. One specimen has a diameter of ninety mm., and includes a por- 

 tion of the grand chamber, occupying about half a volution. A fragment of 

 the chambered portion, incomplete at the apex, measures 130 mm. on the 

 periphery. 



The typical specimen preserves a mammillary deposit upon the surface, 

 apparently connected with the inner laminae of the shell. 



This species is quite distinct from the ordinary forms of Nautilus, and there 

 is little external similarity between them. It is referred to Nautilus on 

 account of the contiguous volutions, the form of the transverse section, the 

 large, apical angle, the comparative size of the chamber of habitation and the 

 chambered portion of the shell, and the absence of any well-defined sinus, while 

 the siphuncle is subcentral. This species is distinguished from the other forms, 

 except N. svbliratus, by the presence of strong, revolving carinae. 



In the typical specimen of N. Urates there are fourteen revolving ridges over 

 the chambered portion of the shell, a part of which become obsolete upon the 

 ventral side of the grand chamber. In the specimen fig. 3 of plate 57 there are 

 nine strong plications seen on the lateral face of a partially compressed grand 

 chamber. 



Formations and localities. In the Goniatite limestone, near Manlius, N. Y. ; 

 and in the shales of the Hamilton group, in Madison county. 



