146 PALAEONTOLOGY OF ILLINOIS. 



above and below by a narrow suture, and a strong revolving 

 carina. Under side of the last volution obliquely flattened; um- 

 bilicus closed. Form of aperture not clearly defined, but appar- 

 ently subovate. Lines of growth are clearly visible on the flat 

 portions of the volutions. Length of a specimen showing seven 

 volutions, 10 / 16 inch; diameter of lower volution % inch. Spiral 

 angle about 20. 



This shell is known only from an imperfect example, and is 

 nearly related to O. salteri, of Meek and Worthen, Vol. II, of 

 these reports, page 381, PI. 31, fig. 14, a, b, c, but differs from 

 that, in its surface ornamentation and its spiral angle. 



Position and locality: Coal Measures, Peoria county, 111. 



Collector, Mr. Gifford. 



No. 2533 of the Illinois State Museum. 



GENUS TRACHYDOMIA. Meek and Worthen. 



TRACHYDOMIA NODULOSA. Worthen. 

 PL XXIII, Figs. 11-lla. 



Trachydomia nodulosa. Worthen, March' 1884. Bulletin No. 2, of the Illinois State 

 Museum of Natural History, page 8. 



Shell of medium size, obliquely ovate or sub-rhomboidal in 

 outline, volutions four, the last one comparatively large and 

 comprising more than two-thirds the entire length, rounded 

 below and slightly flattened above to the nearly perpendicular 

 lower border of the rather deeply impressed suture. Aperture 

 nearly sub-ovate with a well defined notch at its lower ex- 

 tremity; lip sharp, columella flattened and smooth; surface 

 thickly covered with prominent rounded nodes that are largest 

 on the upper edge of the volution, and increase in number as 

 they decrease in size towards the umbilical region. The nodes 

 become obsolete on the lower extremity of the last volution, 

 leaving a limited space around the lip that is ornamented only 

 with a few rather coarse h'nes of growth. 



Length of an average size specimen 10 / 16 inch; breadth 7 / lQ 

 inch. 



