22 PALAEONTOLOGY OF ILLINOIS. 



Cladodus spinosus, N. and W. 



PL 1, Fig. 3, 3 a. 



Teeth, of medium or large size, broader than high; base 

 semi-elliptical, thick, smooth behind where it is brought to a 

 sharpish edge, before strongly beveled under and scooped out 

 in a shallow sinus beneath the median cone; whole anterior 

 border of base, above the smooth beveled edge, set with innu- 

 merable minute spines directed upward; these spines cover the 

 anterior bases of all the lateral denticles, and the base of the 

 principal cone, with the exception of a small triangular space 

 over the centre of the basal sinus, from which they diverge 

 right and left, leaving the striation of the upper portion of the 

 cone to run down nearly to the smooth surface of the beveled 

 edge; median cone conical, somewhat curved backward, 

 rapidly drawn down to an acute point; lower portion with a 

 nearly circular section, finely and evenly striated longitudi- 

 nally ; near the point smooth, compressed, with cutting edges ; 

 lateral denticles 6-7, on either side, conical, striated and curved 

 backward, exterior pair much larger than intermediate ones. 



This beautiful species is readily distinguishable from all that have been 

 described, by its spinous base. Fig. 3, anterior face and section of median cone, 

 3 a, portion of base, under side 



Formation and locality: St. Louis limestone, St. Louis, Missouri. 



Cladodus mortifee, N. and W. 



PI. 1, Fig. 5. 



Only a single tooth, and that much injured, represents this 

 species in the collection ; but that is so obviously distinct from 

 all others, and the characters which it retains are so readily 

 recognizable, that it may, perhaps, justly serve as a basis for a 

 specific description. The summit of the principal cone is 







