

VERTEBRATES. 85 



This beautiful and peculiar tooth is evidently similar in its general character 

 to that described by Prof. Leidy {Jour. Acad. Nat. Sci., Phil., 2d series, Vol. 3, 

 p. 159, pi. 15,) under the name of Edestus vorax, and to those upon the jaw 

 exhibited before the American Association, at the Providence meeting, August, 

 1855. Of the latter we have, as yet, no minute description. From the former 

 it differs in its smaller size, double crenulation and angular base. Whether 

 the jaw to which it was attached was segmented, as in E. vorax, I am not able 

 to say, as but a small portion of it remains in the specimen before me. It was 

 apparently of dense, bony structure, thin and flat. Of the relations of the fish 

 which bore this tooth little can be said, except that it must have been widely 

 different from any forms now living. The crown of the tooth is remarkably 

 like, both in size, form and crenulation, that of the teeth of Hemipristis serra, 

 Agassiz, but the mode of its attachment to the jaw is so different that there 

 could really have been no affinity between them. The teeth of Hemipristis, as 

 well as those of Carcharodon, have osseous, gibbous bases, which were set upon 

 a cartilaginous jaw, to which they had only ligamentous attachment. In the 

 fossil before us the tooth was firmly cemented to a dense bony jaw. On the 

 other hand, to Pristis, with which similar teeth to this one have been compared, 

 it has some slight resemblance, as the teeth of the saw are implanted in a solid 

 bony structure. The fact that they are inserted in cavities is, however, an 

 evidence of a wide difference between Pristis and the fossil before us. As 

 Prof. Agassiz remarked, in reference to the jaw exhibited by Prof. Hitchcock 

 — similar to, if not identical with, our fossil — there is reason to believe that 

 this should be regarded not only as a new genus, but a new family of fishes. 



Figure 24 represents a side view of this tooth, natural side. 



Formation and locality : Coal Measures, Posey county, Indiana. ■ 



Chomatodus costatus, N. and W. 



PI. V, Fig. 17, 11 a. 



Teeth small, laterally elongated, linear in outline; crown 

 surface linear, flattened, truncated at the extremities, slightly 

 arched on one side, straight on the other, with a prominent 

 carina along the arched margin and another straight one con- 

 necting the extremities of the former, like the string to a bow. 

 Along the straight and inferior edge is a ridge marked with 

 elevated spiral lines; the whole surface is smooth and polished, 

 but shows fine pores along the superior costse. The root is 



