06 PALAEONTOLOGY OF ILLINOIS. 



Okodus tuberculatus, N. and W. 



PI. IV, Figs. 9, 9a. 



Teeth small, short, high, conical in outline; median cone 

 relatively large, pointed, sometimes acute; lateral cones rudi- 

 mentary, nearly obsolete, two or three on either side of the 

 principal cone, rapidly diminishing, together forming pointed 

 lateral appendages to the central prominence; central cone 

 bearing several prominent ridges, strongest at the base, fading 

 out at the summit; similar ridges upon the lateral extremities 

 in pairs form the rudimentary secondary cones. On the inside 

 the ridges are less distinct, and are in part represented by 

 enameled tubercles; whole surface of crown polished, and with- 

 out pores. 



The species before us bears a strong resemblance to the preceding one, and 

 indeed to all the smaller species which we have described. It is, however, 

 apparently distinct from all, and may be recognized by its relatively short and 

 high figure, the preponderance of the central over the secondary cones, by its 

 few, strong, ornamental ridges, frequently represented by mere tubercles, etc. 

 Figure 9, crown face seen from above; 9 a, side view, both twice natural size 

 Formation and locality: Burlington limestone, Quincy, Illinois. 



Orodus mammillaris, N. and "W. 



PI. IV, Fig. 10, 10«. 



Teeth small, laterally elongate, slender; crown arched or 

 sub-conical, having a prominent median cone, with a series of 

 2-5 lateral cones on either side; median cone round, as broad 

 as high, the lateral ones more or less appressed and flattened 

 vertically. All these cones are ornamented with numerous, 

 prominent, often beaded ridges, which are strongest at the base 

 and fade out toward the summit on the median and some of 

 the lateral cones. On those near the extremities they meet 

 above. These ridges are strong and rounded; there are about 

 four on either side of the lateral cones and twice as many 



