100 PALAEONTOLOGY OF ILLINOIS. 



Deltodus spatulatus, N. and W. 



PI. IX, Fig. 7. 



Anterior? tooth obliquely spatulate in outline, spirally 

 curved, long and narrow; the broader end obliquely rounded, 

 sides converging to a simple point above, relatively thick; 

 crown surface strongly arched in both directions, without dis- 

 tinct keels or furrows, uniformly granulo-punctate throughout. 



The narrow, crenate form, and simple surface, will enable 

 one to distinguish this species from those with which it is asso- 

 ciated. 



In some of the specimens the base is somewhat broader, and the basal angle 

 common to most species of the genus begins to show itself, while there is a 

 slight depression of the crown along the margin of that side, the representa- 

 tive of the usual furrow. The outline is narrower, however, and more spatu- 

 late, and the whole tooth more simple, than in any other species with which we 

 are acquainted. The punctation of the surface is relatively coarse, and there 

 are raised rings about the orifices of the enameled tubes. Length, 1 inch, 8 

 lines; greatest breadth, 10 lines. 



Figure 7, represents a large and narrow specimen, natural size. 



Formation and locality: Burlington limestone, Quiney, Illinois. 



Deltodus rhomboideus, N. and W. 



PI. IX, Fig. 8. 



Posterior tooth arched, scarcely revolute, sub-rhomboidal in 

 outline, the broader end irregularly rounded, the narrower end 

 obliquely truncated ; the upper surface marked with two nearly 

 parallel, low, obtuse, longitudinal ridges, of which one is mar- 

 ginal, the other central ; the latter being bordered on one side 

 by a shallow furrow separating it from the stronger marginal 

 ridge, on the other by a broader and deeper groove, which 

 occupies the lateral interval between it and the more oblique 

 margins. One or more lines of growth are discernible running 

 parahel with the outline of the broader end ; these produce 



