364 PALEONTOLOGY OF ILLINOIS. 



fishes which inhabited exclusively the Coal Measure seas. It would seem that 

 in the region east of the Mississippi, during the Coal Measure epoch, marine 

 conditions prevailed only locally and for a limited period ; circumstances ap- 

 parently not favorable to the existence of any considerable number of large 

 cartilaginous fishes; for we here find a marked falling off from the rich and 

 diversified ichthyic fauna of the Lower Carboniferous period. 



CYMATODUS OBLONGUS, N. and W. 



PI. iv, fig. 7, 7. 



TEETH of medium or small size (one inch long by three- 

 eighths of an inch wide), oblong or spatulate in* outline, thin, 

 flattened and somewhat arched ; crown surface undulated by 

 relatively large, transverse waves, in all parts and nearly 

 equally dotted by the round or vermicular sections of the ob- 

 lique calcigerous tubes ; under surface parallel to the crown 

 face, smooth throughout the broader portion of the tooth, near 

 the narrow end rising into a long, narrow, strap-shaped, 

 curved root. 



The generalities of the R>rm and structure of this tooth are given in the 

 generic description which is based upon it. It will be seen to have consider- 

 able resemblance to the undulated species of Deltodus, but the transverse waves 

 of the crown surface are more acute-crested, are not curved as in those spe- 

 cies, and no species of Deltodus has the root which forms so conspicuous a fea- 

 ture in this tooth. 



Formation and locality : Upper Coal Measures ; LaSalle, Illinois. 



GENUS COCHLIODUS, Ag. 



COCHLIODUS COSTATUS, N. and W. 



PL iii, fig. 10, 12, 12a. 



TEETH relatively small, very convolute, crown surface bear- 

 ing strongly marked ridges in the line of enrollment ; enam- 

 elled surface uniformly punctate throughout, sometimes with 

 obscure transverse lines of growth ; anterior convolute tooth 



