62 PALAEONTOLOGY OF ILLINOIS. 



Diplodus incurvus, N. and W. 



PI. IV, Fig. 4, 4 a. 



Teeth small ; base large, thin, somewhat spoon-shaped, 

 smooth. From one extremity of this, spring three sub-equal, 

 recurved, divergent, conical denticles. These have a nearly 

 circular section, with a faint lateral angle formed by a fine 

 longitudinal carina; the anterior face of each being somewhat 

 flattened. 



But a single specimen of this singular tooth exists in the collection, and that 

 somewhat broken. Enough of it remains, however, to make out its form fully, 

 and to show its entire distinctness from any species before described. Its pecu- 

 liar character will be seen at a glance by reference to the figures which we give 

 of it. Length of base, 3 lines; breadth in widest part, 2 lines; length of 

 denticles, 1|- lines. 



Figure 4 represents the anterior aspect of the tooth ; figure 4 a, the side 

 view, magnified to two diameters. 



Formation and locality: Keokuk limestone, Nauvoo, Illinois. 



Genus ORODUS, Ag. 



Gen. Char. — "Teeth laterally elongated, having their mid- 

 dle portion more elevated than their extremities, forming in 

 the central portion of the tooth an obtuse and transverse cone; 

 the longitudinal diameter, which much exceeds the transverse, 

 is also marked by a ridge sometimes medial, sometimes sub- 

 medial, from which spring oblique secondary ridges which 

 ramify upon the sides, and which, in the larger teeth, give rise 

 to another series of collateral ridges." 



The genus Orodus has not been before recognized in America. 



Orodus? multicarinatus, N. and "W. 



PI. IV, Fig. 13, 13 a. 



Teeth very large, thick and massive, central portion form- 

 ing a broad, obtuse cone, from which radiate numerous fine 



