78 



PALEONTOLOGY OF ILLINOIS. 



Helodus elytra, N. and W. 



PI. IV, Fig. 23. 



Teeth small, in series of three or more of unequal size. Of 

 these the anterior one is most elongated laterally and highest, 

 the middle one shorter, broader and natter, the posterior one 

 smaller in both senses and flatter than either. They are all 

 oblong in outline, with rounded ends, gently arched both ways, 

 smooth and polished throughout, the surface of each uniformly 

 and relatively coarsely porous. The resemblance which they 

 bear to the elytra of some beetles has suggested the specific 

 name selected. 



Figure 23 represents the series described as seen from above, natural size. 

 Formation and locality : Keokuk limestone, Warsaw, Illinois. 



Helodus compressus, N. anfl W. 



PI. V, Fig. 1. 



Teeth small, much compressed, conical in profile, narrow, 

 linear in outline when seen from above; crown thin, compressed, 

 terminating above in a sub-acute edge, having an obliquely 

 conical outline when seen in profile ; median cone sub-central, 

 the apex being laterally rounded and somewhat inclined toward 

 one of the extremities; ends rounded, narrowed below to the 

 root ; the edge of the crown, between the summit of the cone 

 and the extremity to which it is inclined, faintly notched or 

 waved; anterior and posterior faces of the crown flattened and 

 inclined toward the root; surface highly polished, without pores; 

 root thin, relatively narrow, slightly roughened; breadth 3£ 

 lines, height 2 lines. 



This is a very small species, differing in some important characters from 

 any heretofore described. With the general form of Helodus it is very much 

 more flattened, having almost a cutting edge. It is apparently composed of 

 dense and homogeneous enamel, without pores. In its compressed crown, its 



