222 CEPHALOPODS. 



Horizon and localities. Lower Carboniferous, Ohouteau 

 (Kinderhook) limestone: Sedalia. 



Nautilus digonus MEEK & WORTHEN. 



Nautilus digonus Meek & Worthen, 1866: Geol. Sur. Illinois, vol. Ill, p. 

 458, pi. xiv, figs. 9a-d. 



A small form, with slender volutions, marked by longi- 

 tudinal ribs and transverse lines. 



Horizon and localities. Lower Carboniferous, Kinderhook 

 beds : Callaway county. 



Nautilus spectabilis MEEK & WORTHEN. 



Nautilus spectabilis Meek & Worthen, 1860: Proc. Acad. Nat. Sci. , Phila. , 



p. 469. 

 Nautilus peramplus Meek & Worthen, 1865: Proc. Acad. Nat. Sci., Phila., 



p. 259. 

 Nautilus spectabilis Meek & Worthen, 1866 : Geol. Sur. Illinois, vol. II, 



p. 308, pi. xxv, tigs. la-b. 



A large, robust form with smooth, rounded whorls. 

 Horizon and localities. Lower Carboniferous, Kaekaskia 

 limestone: St. Louis county ( Ham bach). 



Nautilus ponderosus WHITE. 



Nautilus ponderosus White. 1872: U. S. Geol. Sur. Nebraska ( Meek's 

 report), p. 236, pi. iii, figs. 7a-b. 



Shell attaining a large size, subdiscoidal; umbilicus large, 

 or nearly equaling the dorso-ventral diameter of the outer volu- 

 tion near the aperture ; volutions three, enlarging their dia- 

 meter more than three-fold each turn ; all broader transversely 

 than dorso-ventrally ; inner ones slightly embracing, while the 

 last one is apparently merely in contact with the others near 

 the aperture ; each broadly flattened or a little concave on the 

 periphery, and (particularly the last one) somewhat flattened 

 between the periphery and the middle of each side, from which 

 point the sides are broadly rounded into the umbilicus, the 

 greatest transverse diameter being near the middle; ventro- 

 lateral or outer angles of the last whorl (in somewhat worn 

 casts), each provided with obscure traces of about twenty 

 wide, undefined nodes, scarcely perceptible to the eye ; septa 

 numerous, rather closely arranged, making a slight backward 



