FOSSILS OF THE KEOKTJK GROUP. 523 



convexity of whorls, about 1.50 inches; breadth of trun- 

 cated periphery, 0.68 inch. 



In size, form, proportions, breadth of umbilicus, etc., as well as in 

 the arrangement and curvature of its septa, this species seems to agree 

 almost exactly with N". discus, of Sowerby. If that species has been 

 correctly figured and described, however, our shell presents the import- 

 ant difference of having its siphuiicle located a little outside of the 

 middle, instead of near the inner margin of the whorls. 



Locality and position Xiota, Hancock county, Illinois. Keokuk di- 

 vision of the Lower Carboniferous series. 



NAUTILUS (TEMXOCHEILUS) NIOTENSIS, M. and W. 



PL 19, Fig. 3. 

 Nautilus (Temnocheilus) Niotensis, MEEK aud WOKTHBN, 1865. Proceed. Acad. If at. Sci., Phila., p. 260. 



SHELL attaining a large size, globose-subdiscoidal; um- 

 bilicus deep and (considering the lateral carina of the volu- 

 tions on its margin) about twice the dorso-ventral diameter 

 of the outer turn. Volutions about three, contiguous but 

 not embracing, broadly rounded over the dorsal and ventral 

 sides, and prominently angular around the middle of each 

 lateral margin; section transversely elliptic, the two ex- 

 tremities of the ellipse being angular. Septa .rather dis- 

 tinctly concave, and distant on the outer side less than half 

 the dorso-ventral diameter of the whorls, making a broad 

 backward curve in crossing the inner and outer sides of the 

 whorls, and curving forward to each of the lateral angles ; 

 siphon piercing the septa less than its own breadth outside 

 of the middle. Surface and aperture unknown. 



Greatest diameter, measuring across the disc, about 8.50 

 inches; convexity, or transverse diameter of the whorls, 5 

 inches; dorso-ventral diameter of the last volution, about 

 3 inches. 



This species belongs to a group of Carboniferous Nautili, including 

 N. cortHuituv, McCoy, X. biangidatnx, X. multicarinatus and N. carinife- 

 n/s, Sowerby. These shells are characterized by having a broad, deep, 

 open umbilicus, showing all the volutions, with the outer side of the 



