VERTEBRATES. 69 



line, and the raised lines which ornament it are very tortuous and irregular — 

 the larger ones giving off numerous short lateral branches, which give them a 

 pectinated appearance, nothing like which is observable in the epecies before 

 us. In 0. elegantulus a line of bead-like tubercles crown the medial crest, the 

 lines of ornamentation running down upon one side only, while in 0. rninutus 

 both faces of the crown are ornamented. In size the teeth of this species are 

 intermediate between 0. ornatus aud 0. minusculus. 



Figure 12 represents two teeth of a series of four, seen from above, twice the 

 natural size. 



Formation and locality : Keokuk limestone, Nauvoo, Illinois. 



Genus CARCHAROPSIS, Ag. 

 Carcharopsis Wortheni, Newb. 



PI. IV, Figs. 14, 14a. 



Base semi-elliptical in outline, irregularly, coarsely but not 

 deeply scolloped, thick, flattened below, sloped off to the edges 

 above, slightly broader than -the entire height of the tooth; 

 median cone conical, its height about equal to its width, meas- 

 ured across the upper surface of the expanded base; anterior 

 face flattened, posterior regularly rounded, entirely smooth 

 throughout; margins strongly and evenly crenulated from the 

 apex to the base; lateral denticle's two on either side, the exte- 

 rior pair largest, about one-quarter the length of the median 

 cone, situated a little back from the anterior margin, on the 

 extreme points of the base, conical, acute and smooth, and 

 slightly divergent from the axial line of the principal cone; 

 second pair slightly in advance of and within the largest secon- 

 daries, scarcely more than tubercles. Breadth of base, 1 inch, 

 2 lines ; height, apex slightly worn, 1 inch. 



The beautiful tooth from which this description was taken is the first of the 

 genus, so far as we know, that has ever been found on the American continent. 

 Partially covered by the stone it had the appearance of Cladodus, but present- 

 ing some peculiarities, was carefully developed when the elegant crenulation of 



