82 



PALAEONTOLOGY OF ILLINOIS. 



Helodus crenulatis, N. and W. 



PI. V, Fig. 1, 1 a. 



Teeth of medium or large size, outline showing a prominent 

 median angle, the lateral surfaces very unequal in length, 

 somewhat rounded. When seen in profile the outline is also 

 conical, with a prominent angle, but no cone. The crown is 

 arched over transversely, on one side constricted, or the surface 

 turned under; both margins are very neatly crenulated by 

 short, deep, sub-equal sulci; the enameled surface finely and 

 evenly punctate throughout; root very oblique, generally want- 

 ing in the fossil state. 



This is a laterally short and flattened species, readily distinguishable from 

 any other described by its angled outline, when seen from above, and by the 

 distinct crenulation of the crown margins. The specimens we have described 

 were found mingled with fragments of the teeth of Cochliodus, having the same 

 deep black color, and the same microscopic structure. It seems probable there- 

 fore, that both once formed parts of the dentition of the same fish. 



Figure 7, represents the crown as seen from above, natural size ; figure 7 a, 

 under side of same specimen. 



Formation and locality : Keokuk limestone, Warsaw, Illinois. 



Helodus undulatus, N. and W. 



PI. V, Figs. 8, 8a, 8b. 



Teeth medium size, laterally elongated, somewhat bow- 

 shaped in outline, with a prominence before, a sinus behind ; 

 crown conical in outline, the central cone prominent, sub-acute, 

 from this the surface falls off toward either end; upon the 

 lateral portions the enamel is raised into short, broken undula- 

 tions, and tubercles; the porosity is coarse and somewhat irregu- 

 lar, the root is oblique, coarse and bony, showing a nearly ver- 

 tical face posteriorly, two-thirds as high as the crown; from 

 the lower margin of this the under surface slopes upward to 

 the crown on the opposite side. 



