VERTEBRATES. 355 



From C. spinosm, which occurs in the same formation, it is distinguished by 

 its relatively narrower base, fewer lateral denticles, and by its flattened anci- 

 pital central cone. The same characters will serve to separate it from C. mor- 

 tifer and C. ferox, although the former of the last two mentioned approaches 

 it most nearly, and if they occurred in the same deposit it might be suspected 

 that they formed parts of the necessarily somewhat variable dentition of one 

 fish. They are, however, too widely separated geologically, to render this sup- 

 position at all probable. The specimen is in the cabinet of Prof. Litton. 

 Formation and locality : St. Louis limestone ; St. Louis, Mo. 



CLADODTJS DEFLEXUS, N. and W. 



PI. iii, fig. 3, 3a. 



TOOTH of medium size, base as broad as hight of cone, very 

 narrow ; antero-posterior diameter scarcely more than a quar- 

 ter the breadth ; anterior margin straight, posterior regularly 

 arched ; central cone flexed laterally and backward, somewhat 

 flattened and strongly striated in front, rounded and finely 

 striated behind ; lateral denticles, two on each side, relatively 

 large and nearly equal : sometimes there are one or two addi- 

 tional ones of smaller size. 



The laterally deflected median cone, flattened, striated, and angled before, 

 rounded behind, with the very narrow transversely elongated base, will serve 

 as a means of identification of this species wherever found, and to distinguish 

 it from all others of the genus. 



Formation and locality : Burlington limestone ; Quincy, Illinois. 



GENUS PETALODUS. 

 PETALODUS CURTUS, N, and W. 



PI. ill, fig. 2. 



TEETH of moderate size, thin and light in crown and root ; 

 crown broadly arched, twice as wide as high, concavo-convex 

 laterally and vertically ; superior margin serrated or rough- 

 ened by the termini of the calcigerous tubes ; anterior face of 

 crown without imbricating enamel folds, half as high as pos- 



