52 i PALEONTOLOGY OF ILLINOIS. 



whorls broad or flattened, and the middle of each lateral margin promi- 

 nently angular; the angle being sometimes nodose, while the transverse 

 diameter of the volutions is always greater than the dorso-ventral. 

 The siphon in these shells is generally, or perhaps nearly always, be- 

 tween the middle and the outer side of the whorls. Although Prof. 

 McCoY included a much wider range of forms in his group Temnochetttu, 

 it should probably be restricted to such species as those mentioned 

 above, all of which were originally included in the group by Prof. Mo- 

 COY. 



Specifically, our shell is perhaps most nearly allied to Nautilus cari- 

 niferusj of Sowerby, (Min. Conch., p. 482, fig. 3,) though differing in its 

 proportionally wider umbilicus, merely contiguous volutions, and par- 

 ticularly in never having longitudinal ridges on the outer side of the 

 whorls, at any stages of growth. It also differs in having its septa 

 crossing the outer side of the whorls with a broad backward curve, in- 

 stead of passing nearly straight over. 



Locality and position Mota and Warsaw, Illinois; Keokuk division 

 of the Lower Carboniferous. 



NAUTILUS (SOLENOCHEILUS) LEIDYI, M. and W. 



PL 18, Fig. 2. 

 Nautilus Leidyi, MEEK and WOKTHEX, 1865. Proceed. Acad. Nat. Sci., Phila., p. 262. 



THE only specimen of this shell we have seen consists of 

 the non-septate portion, forming about one-third of a volu- 

 tion. It indicates a sub-globose form for the entire shell, 

 and shows that the umbilicus was deep, with rather abrupt 

 walls, and about as broad as three-fourths the dorso-ven- 

 tral diameter of the body whorl at the aperture. From the 

 curve, and rapid increase in the size of the outer chamber, 

 it is evident there could not have been more than about two 

 and a half volutions, which are rather broadly rounded over 

 the dorsum and sides to the margins of the umbilicus, into 

 which the sides round rather abruptly. Towards the aper- 

 ture, the steep, somewhat flattened inner side of the volu- 

 tion forming the walls of the umbilicus meets the lateral 

 margins, so as to form a kind of pinched prominence, that 

 must have imparted a peculiar angularity to the inner 



