68 PALAEONTOLOGY OF ILLINOIS. 



in the same direction; each individual tooth laterally elongated, 

 slender, somewhat arched in outline, strongly so in profile; 

 crown smooth and highly polished throughout, forming an 

 angular ridge, crowned with numerous prominent, bead-like 

 points. Of these the largest is nearer one end than the other; 

 from this point the secondary cones diminish in size to either 

 extremity; lateral length of longest tooth 3 lines; of shortest, 

 1 line; breadth about half a line. 



The teeth which form the basis of the foregoing description retain the rela- 

 tive position which they occupy on the jaw. Like most of the teeth of the 

 genus, they are laterally unsymmetrical, the median cones not being placed on 

 the central point of their longest diameter. Though very minute they are neat 

 and exact in their forms and markings, and undoubtedly are the only traces 

 yet discovered of an entirely distinct species of fish which inhabited the Car- 

 boniferous seas. 



Figure 11 represents the series of teeth described above, magnified to two 

 diameters. 



Formation and locality : Keokuk limestone, Warsaw, Illinois. 



Orodus minutus, N. and "W. 



PI. IV, Fig. 12. 



Teeth very small, forming a series of four or more, increas- 

 ing in size from behind forward; each individual tooth laterally 

 elongated, linear in outline, rounded at one extremity, appa- 

 rently obliquely truncated at the other; crown forming a semi- 

 cylindrical ridge, with a median cone nearest the truncated 

 end. This is worn down in the specimens before us, and its 

 form and relative elevation cannot be determined. The lateral 

 surfaces of the crown exhibit no secondary cones, but the me- 

 dian line is marked by a fine, sharp crest, giving off, nearly at 

 right angles, simple or forked thread-like carinte, which run 

 down to the base. 



This species resembles 0. ornatus and 0. elegantulus more than any others 

 described, but the crown of 0. ornatus is less straight and symmetrical in out- 



