VERTEBEATES. 99 



undulated by broad, transverse, elevated bands separated by 

 narrower sulci, which give an undulated outline to the lateral 

 margins, and to the profile; punctation of the upper surface 

 strongly marked throughout. Length, 2 inches; greatest 

 breadth, 1 inch, 3 lines. 



This beautiful species may be at once recognized by its highly polished and 

 shining surface, and its broad, transverse undulation. Pcecilodus sublsevis, 

 McCoy, is somewhat like it, but is smaller, less strongly marked by the trans- 

 verse ridges and sulci, and with a less deep longitudinal furrow. 



Figure 5, represents the upper surface, natural size. 



Formation and locality: Keokuk limestone, Keokuk, Iowa. 



Deltodus cingulatus, N. and "W. 



PI. IX, Fig. 6. 



Teeth narrow, wedge-shaped in outline, spirally enrolled, 

 the broader end obliquely rounded; triturating surface trans- 

 versely arched, marked with numerous conspicuous, obliquely 

 transverse, sub-equal ridges or belts of enamel, separated by 

 parallel furrows of nearly equal width ; the surface of the fur- 

 rows is coarsely porous and reticulated, that of the ridges very 

 finely and evenly punctate. 



In this species we have an extreme instance of the division of the triturating 

 surface into bands of unequal hardness, which constitute the distinctive char- 

 acter of Poecilodus. Here the surface is divided into broad, transverse, zone- 

 like bands, more than a line in width ; alternations of hard, dense, smooth 

 enamel, and coarse, reticulated bone. The bands of harder material are most 

 prominent, and give to the profile an undulated outline. This interesting tooth 

 will, doubtless, be ultimately separated from Deltodus and placed in a genus 

 created to receive it and its more immediate congeners. Without more material, 

 however, we refrain from attempting to define the characters and limits of such 

 a genus. 



Figure 6, represents the crown surface, natural size. 



Formation and locality : Chester limestone, Chester, Illinois. 



