INVERTEBRATES. 145 



Shell about the medium size, consisting of about five moder- 

 ately convex volutions, the last one constituting more than 

 one-half the entire length. The volutions taper gradually, and 

 present no indications of external ornamentation. 



Exact form of aperture unknown. Length of the four volu- 

 tions preserved, 2% inches; length of last volution, 1% inches; 

 breadth of the same where it seems to be somewhat flattened 

 by pressure, % inch. 



Collector, Mr. L. A. Cox, of Keokuk. 

 No. 2494 of the Illinois State Museum. 



GENUS DENTALIUM. Linnams. 

 DENTALIUM ILLINOIENSE. Worthen. 



PL XXIII, Fig. 1. 

 Dentallum illinoiense, Worthen, 1883. GeoL Surv. of Illinois. VoL VII, page 325. 



Shell above a medium size, long, straight, cylindrical, slightly 

 tapering, scarcely inflated at the aperture. Surface apparently 

 smooth originally, but slightly roughened by weathering in the 

 specimen under examination. 



Length 5% inches; width near the aperture, 7 /io inch. 

 This species differs from D. missouriense of Swallow, in its 

 larger size, smooth surface and straight form. 

 Position and locality: Chester limestone, Chester, 111. 

 Collector, A. H. Worthen. 

 No. 2488 of the Illinois State Museum. 



GENUS ORTHONEMA. Meek and Worthen. 



ORTHONEMA CARBONARIUM. Worthen. 

 PL XXIV, Figs. 4-4a. 



Orthonema carbonaria, Worthen, March, 1884. Bulletin No. 2, of the Illinois State 

 Museum of Natural History, page 7. 



Shell very elongate, gradually tapering from the base to the 

 apex, with nine or more flattened volutions that are defined 

 18 



